tests: add simple kv check app

This is helpful for users to quickly check if they have KV support or
not.

examples/tests/kv_check/Makefile

@@ -0,0 +1,11 @@
+# Makefile for user application
+
+# Specify this directory relative to the current application.
+TOCK_USERLAND_BASE_DIR = ../../..
+
+# Which files to compile.
+C_SRCS := $(wildcard *.c)
+
+# Include userland master makefile. Contains rules and flags for actually
+# building the application.
+include $(TOCK_USERLAND_BASE_DIR)/AppMakefile.mk

examples/tests/kv_check/README.md

@@ -0,0 +1,55 @@
+KV Check
+=========
+
+This is a simple application to check for the presence of Key-Value support or
+not.
+
+If KV support exists, you should see:
+
+```
+[KV] Check for Key-Value Support
+Key-Value support is enabled.
+```
+
+and if you have the process console enabled:
+
+```
+$ tockloader listen
+tock$ process kv_check
+𝐀𝐩𝐩: kv_check   -   [Terminated]
+ Events Queued: 0   Syscall Count: 17   Dropped Upcall Count: 0
+ Restart Count: 0
+ Last Syscall: Exit { which: 0, completion_code: 0 }
+ Completion Code: 0
+ Credential: None
+
+
+ ╔═══════════╤══════════════════════════════════════════╗
+ ║  Address  │ Region Name    Used | Allocated (bytes)  ║
+ ╚0x2000B000═╪══════════════════════════════════════════╝
+             │ Grant Ptrs      128
+             │ Upcalls         320
+             │ Process         920
+  0x2000AAA8 ┼───────────────────────────────────────────
+             │ ▼ Grant          76
+  0x2000AA5C ┼───────────────────────────────────────────
+             │ Unused
+  0x20009FC8 ┼───────────────────────────────────────────
+             │ ▲ Heap         1100 |   3808               S
+  0x20009B7C ┼─────────────────────────────────────────── R
+             │ Data            892 |    892               A
+  0x20009800 ┼─────────────────────────────────────────── M
+             │ ▼ Stack         240 |   2048
+  0x20009710 ┼───────────────────────────────────────────
+             │ Unused
+  0x20009000 ┴───────────────────────────────────────────
+             .....
+  0x00042000 ┬─────────────────────────────────────────── F
+             │ App Flash      8116                        L
+  0x0004004C ┼─────────────────────────────────────────── A
+             │ Protected        76                        S
+  0x00040000 ┴─────────────────────────────────────────── H
+```
+
+note that `Completion Code` is zero, meaning KV support exists. If not, the
+completion code will be -1.

examples/tests/kv_check/main.c

@@ -0,0 +1,19 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <console.h>
+#include <kv.h>
+
+int main(void) {
+  printf("[KV] Check for Key-Value Support\n");
+
+  if (kv_check_status() == RETURNCODE_SUCCESS) {
+    printf("Key-Value support is enabled.\n");
+    tock_exit(0);
+  } else {
+    printf("[ERROR] Key-Value support is NOT enabled.\n");
+    tock_exit(-1);
+  }
+
+  return 0;
+}