drm/i915: Keep PSR disabled after a driver reload after a PSR error

If a PSR error happened and the driver is reloaded, the EDP_PSR_IIR
will still keep the error set even after the reset done in the
irq_preinstall and irq_uninstall hooks.
And enabling in this situation cause the screen to freeze in the
first time that PSR HW tries to activate so lets keep PSR disabled
to avoid any rendering problems.

v5: rebased: using edp_psr_shift()

v4: Moved handling from intel_psr_compute_config() to
intel_psr_init() to avoid hardware access during compute(Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: 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>

squash
Link: https://patchwork.freedesktop.org/patch/msgid/20181121225441.18785-5-jose.souza@intel.com