MIPS: asm: uaccess: Add EVA support to copy_{in, to,from}_user

Use the EVA specific functions from memcpy.S to perform
userspace operations. When get_fs() == get_ds() the usual load/store
instructions are used because the destination address is located in
the kernel address space region. Otherwise, the EVA specifc load/store
instructions are used which will go through th TLB to perform the virtual
to physical translation for the userspace address.

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