powerpc: Annotate endianness of various variables and functions

powerpc: Annotate endianness of various variables and functions

Sparse reports several endianness warnings on variables and functions
that are consistently treated as big endian. There are no
multi-endianness shenanigans going on here so fix these low hanging
fruit up in one patch.

All changes are just type annotations; no endianness switching
operations are introduced by this patch.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231011053711.93427-7-bgray@linux.ibm.com