This is easier to deal with when using generic code since it allows us to
use a register index instead of naming each register.
Adjust it, adding an enum to improve readability.
Signed-off-by: Simon Glass <sjg@chromium.org>
PMU is the power management unit and GRF is the general register file. Both
are heavily used in U-Boot. Add header files with register definitions.
Signed-off-by: Simon Glass <sjg@chromium.org>