drm/i915/psr: Remove wait_for_idle() for PSR2

CI runs show PSR2 does not go to IDLE with selective update enabled on
all PSR exit triggers. Specifically, logs indicate the hardware enters
"SLEEP Selective Update" and not "IDLE Reset state', like the kernel
expects, when vblank interrupts are enabled. This check was added for PSR1
but incorrectly extended to PSR2, remove the check as it breaks tests
and prints out misleading error messages.

v2: Split out non-code changes (Rodrigo)

Cc: Tarun Vyas <tarun.vyas@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Fixes: c43dbcbb ("drm/i915/psr: Lockless version of psr_wait_for_idle")
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180824230844.12428-1-dhinakaran.pandiyan@intel.com