MIPS: BMIPS: Add early CPU initialization code

MIPS: BMIPS: Add early CPU initialization code

Port the stblinux-3.3 code to perform a bunch of CPU-specific initialization,
make it compatible with run-time detection of the CPU, and unroll the
brcmstb-specific macros: BDEV_RB(), BDEV_UNSET.

The "pref 30" disabling is done as a quirk. This is a preliminary change to
allow the use of the "rotr" instruction gated by cpu_has_rixi.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: john@phrozen.org
Cc: cernekee@gmail.com
Cc: jon.fraser@broadcom.com
Cc: pgynther@google.com
Cc: paul.burton@imgtec.com
Cc: ddaney.cavm@gmail.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12504/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>