drm/hyperv : Removing the restruction of VRAM allocation with PCI bar size

There were two different approaches getting used in this driver to
allocate vram:
	1. VRAM allocation from PCI region for Gen1
	2. VRAM alloaction from MMIO region for Gen2
First approach limilts the vram to PCI BAR size, which is 64 MB in most
legacy systems. This limits the maximum resolution to be restricted to
64 MB size, and with recent conclusion on fbdev issue its concluded to have
similar allocation strategy for both Gen1 and Gen2. This patch unifies
the Gen1 and Gen2 vram allocation strategy.

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: Deepak Rawat <drawat.floss@gmail.com>
Link: https://lore.kernel.org/r/1653143019-20032-1-git-send-email-ssengar@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>