drm/i915/psr: fix blank screen issue for psr2

Psr1 and psr2 are mutually exclusive,ie when psr2 is enabled,
psr1 should be disabled.When psr2 is exited , bit 31 of reg
PSR2_CTL must be set to 0 but currently bit 31 of SRD_CTL
(psr1 control register)is set to 0.
Also ,PSR2_IDLE state is looked up from SRD_STATUS(psr1 register)
instead of PSR2_STATUS register, which has wrong data, resulting
in blankscreen.
hsw_enable_source is split into hsw_enable_source_psr1 and
hsw_enable_source_psr2 for easier code review and maintenance,
as suggested by rodrigo and jim.

v2: (Rodrigo)
- Rename hsw_enable_source_psr* to intel_enable_source_psr*

v3: (Rodrigo)
- In hsw_psr_disable ,
  1) for psr active case, handle psr2 followed by psr1.
  2) psr inactive case, handle psr2 followed by psr1

v4:(Rodrigo)
- move psr2 restriction(32X20) to match_conditions function
  returning false and fully blocking PSR to a new patch before
  this one.

v5: in source_psr2, removed val = EDP_PSR_ENABLE

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jim Bride <jim.bride@linux.intel.com>
Signed-off-by: Vathsala Nagaraju <vathsala.nagaraju@intel.com>
Signed-off-by: Patil Deepti <deepti.patil@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1484244059-9201-1-git-send-email-vathsala.nagaraju@intel.com