MIPS: lib: memcpy: Add EVA support

Add copy_{to,from,in}_user when the CPU operates in EVA mode.
This is necessary so the EVA specific instructions can be used
to perform the virtual to physical translation for user space
addresses. We will use the non-EVA functions to read from kernel
if needed.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>