hwc: allow DMA pipe in BLOCK mode for virtual dpy

For portrait videos case on WFD, driver supports multiplexing
of DMA pipe in LINE and BLOCK mode.
Loosen the requirements to allow DMA pipe in block mode for
portrait case of virtual display.

Change-Id: I5821501f89b17bb2d29c425aee0a6c16b2a4783b
3 files changed