powerpc/code-patching: Test patch_instructions() during boot

patch_instructions() introduces new behaviour with a couple of
variations. Test each case of

  * a repeated 32-bit instruction,
  * a repeated 64-bit instruction (ppc64), and
  * a copied sequence of instructions

for both on a single page and when it crosses a page boundary.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240325052815.854044-1-bgray@linux.ibm.com