sh: Optimise memcpy_to/fromio for SH4

Optimise memcpy_to/fromio. This is used extensivly by MTD, so is a
worthwhile performance gain. The main savings come from not repeatedly
calling readl/writel, and doing word instead of byte at a time
transfers. Also using "movca.l" on SH4 gives a small performance win.

Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>