Add offset & mask fields to struct powerdomain

In case of AM33xx family of devices, there is no consistency between
PWRSTCTRL & PWRSTST register offsers in PRM space, for example -

PRM_XXX           PWRSTCTRL     PWRSTST
=======================================
PRM_PER_MOD:      0x0C,         0x08
PRM_WKUP_MOD:     0x04,         0x08
PRM_MPU_MOD:      0x00,         0x04
PRM_DEVICE_MOD:   NA,           NA

And also, there is no consistency between bit-offsets inside
PWRSTCTRL & PWRSTST register, for example -

PRM_XXX           LOGICRET  MEMON  MEMRET
=======================================
GFX_PWRCTRL:      2,        17,    6
PER_PWRCTRL:      3,        25,    29
MPU_PWRCTRL:      2,        18,    22
WKUP_PWRCTRL:     3,        NA,    NA

This means, we need to maintain and pass on all this information
in powerdomain handle; so adding fields for,
   - PWRSTCTRL/ST register offset
   - Logic retention state mask
   - mem_on/ret/pwrst/retst mask

Currently, this fields is only applicable and used for AM33XX devices.
Signed-off-by: Vaibhav Hiremath <hvaibhav@ti.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Rajendra Nayak <rnayak@ti.com>
[paul@pwsan.com: this patch is a combination of "Add offset & mask fields to
 struct powerdomain" and the powerdomain portions of "ARM: OMAP3+: am33xx:
 Add powerdomain & PRM support"; updated for 3.5]
Signed-off-by: Paul Walmsley <paul@pwsan.com>