ARM: move AES typedefs and function prototypes to separate header

Put the struct definitions for AES keys and the asm function prototypes in a
separate header and export the asm functions from the module.
This allows other drivers to use them directly.

Change-Id: Iac2b957812d676cea73199bfd15536c64c66a9cf
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>