MIPS: lib: memcpy: Merge EXC and load/store macros

Each load/store macro always adds an entry to the __ex_table
using the EXC macro. Therefore, these load/store macros are now merged
with the EXC one. The argument list is also expanded in order to make
the macro more flexible. The extra 'type' argument is not used by this
commit, but it will be used when the EVA support is added to the memcpy.

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