powerpc/breakpoint: Cleanup

cache_op_size() does exactly the same as l1_dcache_bytes().

Remove it.

MSR_64BIT already exists, no need to enclode the check
around #ifdef __powerpc64__

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/6184b08088312a7d787d450eb902584e4ae77f7a.1632317816.git.christophe.leroy@csgroup.eu