MIPS: lib: strlen_user: Use macro to build the strlen_user symbol

Build the __strlen_user symbol using a macro. In EVA mode we will
need to use similar code to do the userspace load operations so
it is better if we use a macro to avoid code duplications.

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

diff --cc arch/mips/lib/strlen_user.S
Simple merge