docs: powerpc: fix indentation warnings

Sphinx reported unexpected indentation warnings:

Documentation/powerpc/elf_hwcaps.rst:82: WARNING: Unexpected indentation.
Documentation/powerpc/elf_hwcaps.rst:100: WARNING: Unexpected indentation.
Documentation/powerpc/elf_hwcaps.rst:117: WARNING: Unexpected indentation.
Documentation/powerpc/elf_hwcaps.rst:122: WARNING: Unexpected indentation.
Documentation/powerpc/elf_hwcaps.rst:144: WARNING: Unexpected indentation.

Fix these warnings by unindenting commit references and using literal code
block for instructions list for PPC_FEATURE_ICACHE_SNOOP.

Fixes: 3df1ff42e69e91 ("powerpc: add documentation for HWCAPs")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/linuxppc-dev/20220727220050.549db613@canb.auug.org.au/
Link: https://lore.kernel.org/r/20220728033332.27836-2-bagasdotme@gmail.com