drm/i915/display: Fix handling of enable_psr parameter

Commit 3cf05076 ("drm/i915/bios: Split VBT data into per-panel vs.
global parts") cause PSR to be disabled when enable_psr has the
default value and there is at least one DP port that do not supports
PSR.

That was happening because intel_psr_init() is called for every DP
port and then enable_psr is globaly set to 0 based on the PSR support
of the DP port.

Here dropping the enable_psr overwritten and using the VBT PSR value
when enable_psr is set as default.

Fixes: 3cf05076 ("drm/i915/bios: Split VBT data into per-panel vs. global parts")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Jouni Högander <jouni.hogander@intel.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220608203344.513082-1-jose.souza@intel.com