lib: Add shared copies of some GCC library routines ...

This commit is based on these linux kernel commits:

| commit b35cd98
| Author: Palmer Dabbelt <palmer@dabbelt.com>
| Date:   Tue May 23 10:28:26 2017 -0700
|
|     lib: Add shared copies of some GCC library routines
|
| commit e3d5980
| Author: Matt Redfearn <matt.redfearn@mips.com>
| Date:   Wed Apr 11 08:50:17 2018 +0100
|
|     lib: Rename compiler intrinsic selects to GENERIC_LIB_*

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>