crypto: x86/sha256-avx - Fix RBP usage

crypto: x86/sha256-avx - Fix RBP usage

Using RBP as a temporary register breaks frame pointer convention and
breaks stack traces when unwinding from an interrupt in the crypto code.

Swap the usages of R12 and RBP.  Use R12 for the TBL register, and use
RBP to store the pre-aligned stack pointer.

Reported-by: Eric Biggers <[email protected]>
Reported-by: Peter Zijlstra <[email protected]>
Tested-by: Eric Biggers <[email protected]>
Acked-by: Eric Biggers <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>