sh: Add unaligned memory access for PC relative intructions

This adds unaligned memory access support for the following instructions:
  mov.w @(disp,PC),Rn
  mov.l @(disp,PC),Rn

These instructions are often used on SH2A toolchains.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>