powerpc/64/asm: Inline BRANCH_TO_C000

It is used just once and does not really help with readability, remove it.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211221055904.555763-4-aik@ozlabs.ru