drm/display: Add missing Adaptive Sync DPCD definitions

The missing DPCD definitions from DP2.0 spec is as follows:

DOWNSPREAD_CTRL (107h):
	FIXED_VTOTAL_AS_SDP_EN_IN_PR_ACTIVE (bit 6)
		For sink devices that support Adaptive-Sync operation
		and Panel Replay

DPRX_FEATURE_ENUMERATION_LIST_CONT_1 (2214h):
	ADAPTIVE_SYNC_SDP_SUPPORTED (bit 0)
		Bit to check sink device has Adaptive-Sync capability
	AS_SDP_FIRST_HALF_LINE_OR_3840_PIXEL_CYCLE_WINDOW_NOT_SUPPORTED (bit 1)
		A sink device that clears this bit will generate VSync pulse
		leading edge of the HDMI output on the line count at which
		Adaptive-Sync SDP is received as long as source device transmits
		Adaptive-Sync SDP either in first line or first 3840 pixel cycles
		of the line whichever occurs first.
	VSC_EXT_SDP_FRAMEWORK_VERSION_1_SUPPORTED (bit 4)
		Bit to check sink device has SDP framework version 1 capability

Signed-off-by: Sung Joon Kim <Sungjoon.Kim@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>