MIPS: Use generic GCC library routines from lib/

The commit b35cd988 ("lib: Add shared copies of some GCC library
routines") makes it possible to share generic GCC library routines by
several architectures.

This commit removes several generic GCC library routines from
arch/mips/lib/ in favour of similar routines from lib/.

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
[Matt Redfearn] Use GENERIC_LIB_* named Kconfig entries
Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/19051/


Signed-off-by: James Hogan <jhogan@kernel.org>