powerpc: ABIv2 function calls must place target address in r12

To establish addressability quickly, ABIv2 requires the target
address of the function being called to be in r12. Fix a number of
places in assembly code that we do indirect function calls.

We need to avoid function descriptors on ABIv2 too.

Signed-off-by: Anton Blanchard <anton@samba.org>

diff --cc arch/powerpc/kernel/entry_64.S
Simple merge

diff --cc arch/powerpc/kernel/head_64.S
Simple merge

diff --cc arch/powerpc/kernel/misc_64.S
Simple merge