drm/amd/display: Update chip_cap defines and usage

[WHY]
The defines have also been updated with prefix AMD_ and atomfirmware.h
has been temporarily updated with both sets of defines to allow the
transition.
This update is being made to standardize workaround chip_cap flags,
in order to support more workaround flags in the future.

[HOW]
Updated EXT_DISPLAY_PATH_CAPS__DP_FIXED_VS_EN define, the flag is now
an enum masked by EXT_DISPLAY_PATH_CAPS__EXT_CHIP_MASK. All checks for
DP_FIXED_VS_EN are now performed by masking with EXT_CHIP_MASK and
checking for an exact match rather than the previous bitwise AND check.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>