drm/i915: Check EDID for HDR static metadata when choosing blc

We have now seen panel (XMG Core 15 e21 laptop) advertizing support
for Intel proprietary eDP backlight control via DPCD registers, but
actually working only with legacy pwm control.

This patch adds panel EDID check for possible HDR static metadata and
Intel proprietary eDP backlight control is used only if that exists.
Missing HDR static metadata is ignored if user specifically asks for
Intel proprietary eDP backlight control via enable_dpcd_backlight
parameter.

v2 :
- Ignore missing HDR static metadata if Intel proprietary eDP
  backlight control is forced via i915.enable_dpcd_backlight
- Printout info message if panel is missing HDR static metadata and
  support for Intel proprietary eDP backlight control is detected

Fixes: 4a8d79901d5b ("drm/i915/dp: Enable Intel's HDR backlight interface (only SDR for now)")
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5284
Cc: Lyude Paul <[email protected]>
Cc: Mika Kahola <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Filippo Falezza <[email protected]>
Cc: [email protected]
Signed-off-by: Jouni Högander <[email protected]>
Signed-off-by: Ville Syrjälä <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Lyude Paul <[email protected]>
(cherry picked from commit b4b157577cb1de13bee8bebc3576f1de6799a921)
Signed-off-by: Joonas Lahtinen <[email protected]>

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