sdm: Use FB resolution for virtual display

For setting virtual display attributes, use FrameBuffer
resolution instead of output buffer width and height.
This is needed to avoid scaling for FBT layer, as output
buffer width and height will be aligned and may differ
from virtual display resolution.
E.g.: In case of 1080p virtual display
Output buffer size - 1920 x 1088
FrameBuffer size - 1920 x 1080

Change-Id: I38b5be10c2797266eff081901d4d482e043047de
1 file changed