Support partitioning of hybrid boot disks

Anaconda needs to be able to create hybrid boot disks. For example:

  clearpart --all --initlabel --disklabel=gpt
  part prepboot  --size=4    --fstype=prepboot
  part biosboot  --size=1    --fstype=biosboot
  part /boot/efi --size=100  --fstype=efi
  part /boot     --size=1000 --fstype=ext4 --label=boot
  part /         --grow      --fstype xfs

However, this kickstart snippet is not working with two or more disks.
The bootloader-related partitions should be all created on the disk
the computer will boot from, but Blivet does that only for platform
-specific partitions. The rest of them are created on any disk with
enough space.

It looks like this can be easily fixed by setting the same weight
to all of these partitions regardless of the current platform.

See: rhinstaller/anaconda#5298

blivet/devices/partition.py

@@ -454,24 +454,19 @@ def _get_weight(self):
 
         # now we have the weights for varying mountpoints and fstypes by platform
         weight = 0
+
         if self.format.mountable and self.format.mountpoint == "/boot":
             weight = 2000
         elif (self.format.mountable and
               self.format.mountpoint == "/boot/efi" and
-              self.format.type in ("efi", "macefi") and
-              arch.is_efi()):
+              self.format.type in ("efi", "macefi")):
             weight = 5000
-        elif arch.is_x86() and self.format.type == "biosboot" and not arch.is_efi():
+        elif self.format.type in ("biosboot", "appleboot", "prepboot"):
             weight = 5000
         elif self.format.mountable and arch.is_arm():
             # On ARM images '/' must be the last partition.
             if self.format.mountpoint == "/":
                 weight = -100
-        elif arch.is_ppc():
-            if arch.is_pmac() and self.format.type == "appleboot":
-                weight = 5000
-            elif arch.is_ipseries() and self.format.type == "prepboot":
-                weight = 5000
 
         return weight