arm64: Change memcpy in kernel to use the copy template file

This converts the memcpy.S to use the copy template file. The copy
template file was based originally on the memcpy.S

Signed-off-by: Feng Kan <fkan@apm.com>
Signed-off-by: Balamurugan Shanmugam <bshanmugam@apm.com>
[catalin.marinas@arm.com: removed tmp3(w) .req statements as they are not used]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

(cherry picked from commit e5c88e3f2fb35dca5f3e46d65095bf5d008595b7)
Signed-off-by: Alex Shi <alex.shi@linaro.org>