crypto: x86/sha256-avx2 - Fix RBP usage

crypto: x86/sha256-avx2 - 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.

There's no need to use RBP as a temporary register for the TBL value,
because it always stores the same value: the address of the K256 table.
Instead just reference the address of K256 directly.

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]>