drm/dp: add extended receiver capability field present bit

drm/dp: add extended receiver capability field present bit

This bit was added to DP Training Aux RD interval with DP 1.3. Via
descriptiion of the spec this field indicates the panels true
capabilities are described in DPCD address space 02200h through 022FFh.

v2: version comment update
v3: version comment correction, commit message update
v4: white space correction

Signed-off-by: Matt Atwood <matthew.s.atwood@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
[manasi: fixup whitespace per Rodrigo's comment]
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180723212735.23893-1-matthew.s.atwood@intel.com