drm/i915/backlight: Remove DP_EDP_BACKLIGHT_AUX_ENABLE_CAP check for DPCD backlight

drm/i915/backlight: Remove DP_EDP_BACKLIGHT_AUX_ENABLE_CAP check for DPCD backlight

Turns out some panels allow only AUX based backlight
by just setting the DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP and
not setting the DP_EDP_BACKLIGHT_AUX_ENABLE_CAP.
If we make DP_EDP_BACKLIGHT_AUX_ENABLE_CAP a necessity for AUX
based DPCD backlight these panels loose the ability to manipulate
backlight via AUX, especially ones with no PWM controller.
Remove this check from function so that panels who do not advertise
DP_EDP_BACKLIGHT_AUX_ENABLE_CAP but advertise
DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP are able to manipulate
backlight again.

Fixes: ed8be780bdbc ("drm/i915/backlight: Fix VESA backlight possible check condition")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16507
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Michał Grzelak <michal.grzelak@intel.com>
Link: https://patch.msgid.link/20260716030959.436430-1-suraj.kandpal@intel.com
(cherry picked from commit 7d594b24c915afb4b0c5fb8875403253daef5b24)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>