Bring RPM out of reset on initial boot-up

Looking closer at the Linux kernel log I notice that all RPM regulators
seem to be suddenly broken:

  adv7511 3-0039: failed to init regulators

Poking some registers it looks like RPM is still in reset, because
0x1860000 (GCC_APSS_MISC) still has the reset bit set. Apparently,
the HYP firmware is also responsible for bringing RPM out of reset
on the initial boot-up.

Implementing this isn't that hard, so add some additional assembly
to store if this is the initial boot and clear the reset bit
if necessary.

This makes the RPM regulators work again! :)

qhypstub.ld

@@ -8,4 +8,5 @@ SECTIONS {
 	. = 0x86400000;
 
 	.text : { *(.text) }
+	.data : { *(.data) }
 }

qhypstub.s

@@ -7,6 +7,7 @@
  */
 .cpu	cortex-a53
 
+.equ	STATE_INITIAL,	0
 .equ	STATE_AARCH32,	1
 .equ	STATE_AARCH64,	2
 
@@ -39,6 +40,7 @@ _start:
 	 * Register allocation:
 	 *   x0 = temporary register
 	 *   x1 = STATE_AARCH32/STATE_AARCH64
+	 *   x2 = execution_state value
 	 *   x3 = temporary register
 	 *   lr = bootloader/kernel entry address
 	 */
@@ -50,6 +52,19 @@ _start:
 		mov	x3, xzr
 	.endm
 
+	/* First, figure out if this is the initial boot-up */
+	adr	x0, execution_state
+	ldrb	w2, [x0]
+	cbnz	w2, skip_init
+	strb	w1, [x0]	/* set initial execution_state based on x1 */
+
+	/* Bring RPM out of reset */
+	mov	x0, 0x1860000	/* GCC_APSS_MISC */
+	ldr	w3, [x0]
+	and	w3, w3, ~0b1	/* RPM_RESET_REMOVAL */
+	str	w3, [x0]
+
+skip_init:
 	cmp	x1, STATE_AARCH64
 	bne	not_aarch64
 
@@ -83,3 +98,7 @@ not_aarch64:
 
 panic:
 	b	panic
+
+.data
+execution_state:
+	.byte	0