sh: sh2a: Add missing #include <asm/processor.h>

arch/sh/kernel/cpu/sh2a/opcode_helper.c:34:14: warning: no previous prototype for 'instruction_size' [-Wmissing-prototypes]

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/8314dd9a966394dd1fd82d88095c57d9778fcfc9.1709326528.git.geert+renesas@glider.be


Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>