ARM: OMAP2/3: PRM: fix bogus OMAP2xxx powerstate return values

On OMAP2xxx chips, the register bitfields for the
PM_PWSTCTRL_*.POWERSTATE and PM_PWSTST_*.LASTSTATEENTERED are
different than those used on OMAP3/4.  The order is reversed.  So, for
example, on OMAP2xxx, 0x0 indicates 'ON'; but on OMAP3/4, 0x0
indicates 'OFF'.  Similarly, on OMAP2xxx, 0x3 indicates 'OFF', but on
OMAP3/4, 0x3 indicates 'ON'.

To fix this, we treat the OMAP3/4 values as the powerdomain API
values, and create new low-level powerdomain functions for the
OMAP2xxx chips which translate between the OMAP2xxx values and the
OMAP3/4 values.

Without this patch, the conversion of the OMAP2xxx PM code to the
functional powerstate code results in a non-booting kernel.

Signed-off-by: Paul Walmsley <paul@pwsan.com>