Create separate .S-file for common support functions

Create kai_common_sme_asm.S to hold support functions that uses pure assembly
instead of inlined assembly.

The function moved in this patch is kai_get_sme_vector_length_u8.

Signed-off-by: Jens Elofsson <jens.elofsson@arm.com>

Approved-by: Jakub Sujak <jakub.sujak@arm.com>
Approved-by: Anton Bondarenko <anton.bondarenko@arm.com>