MLK-12495 mx6: Add LDO bypass support

MLK-12495 mx6: Add LDO bypass support

Port LDO bypass support from v2015 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 5b87d04dba66fa45375d59648838ef89f559f75d)