drm: When adding probed modes, preserve duplicate mode types

The code which takes probed modes and adds them to a connector eliminates
duplicate modes by comparing them using drm_mode_equal. That function
doesn't consider the type bits, which means that any modes which differ only
in the type field will be lost.

One of the bits in the mode->type field is the DRM_MODE_TYPE_PREFERRED bit.
If the mode with that bit is lost, then higher level code will not know
which mode to select, causing a random mode to be used instead.

This patch simply merges the two mode type bits together; that seems
reasonable to me, but perhaps only a subset of the bits should be used? None
of these can be user defined as they all come from looking at just the
hardware.

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>