MLK-12495 mx6: Add LDO bypass support to i.MX6 SOC

MLK-12495 mx6: Add LDO bypass support to i.MX6 SOC

Port LDO bypass SOC codes from v2017 to support the features:

1. Add check for 1.2GHz core speed. If Speed grading fuse is for 1.2GHz,
   enable LDO bypass and setup PMIC voltages. LDO bypass is dependent
   on the flatten device tree file.

2. We set WDOG_B in set_anatop_bypass() before, because it is the only case, but now
   on i.mx6sabreauto board, we didn't use ldo-bypass mode, but have to use WDOG_B to
   reboot whole board, so split these code to independent function so that board file
   can call it freely.

Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit 6bceaf009718cec856e11106d26e13601631fa4f)