drm/i915: Disable PSR2 while getting pipe CRC

When PSR2 is active aka after the number of frames programmed in
PSR2_CTL 'Frames Before SU Entry' hardware stops to generate CRC
interrupts causing IGT tests to fail due timeout.

This same behavior don't happen with PSR1, as soon as pipe CRC is
enabled it blocks PSR1 activation so CRC calculation continues to
happens normaly.

This patch also set mode_changed as true when PSR is available to
force atomic check functions to compute new PSR state, otherwise PSR2
would not be disabled.

v4: Only setting mode_changed if has_psr is set(Dhinakaran)

v3: Reusing intel_crtc_crc_prepare() and crc_enabled, only setting
mode_changed if it can do PSR.

v2: Changed commit description to describe that PSR2 inhibit CRC
calculations.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190308000050.6226-6-jose.souza@intel.com