OvmfPkg/Bhyve: use static PCI32Base address

OvmfPkg/Bhyve: use static PCI32Base address

It's neccessary to allocate a Graphics Stolen Memory area to enable
GPU-Passthrough for integrated Intel GPUs. Therefore, use a new
memory layout with a static Pci32Baseaddress.

Old layout:
	[...        , lowmemlimit] RAM
	[lowmemlimit, 0xE000 0000] PCI Space
New layout:
	[...        , lowmemlimit] RAM
	[lowmemlimit, gsmbase    ] Memory hole (may be absent)
	[gsmbase    , 0xC000 0000] GSM (may be absent)
	[0xC000 0000, 0xE000 0000] PCI Space

Reviewed-by: Peter Grehan <grehan@freebsd.org>
Acked-by: Rebecca Cran <rebecca@bsdio.com>
Signed-off-by: Corvin Köhne <c.koehne@beckhoff.com>
Message-Id: <20210705110842.14088-2-c.koehne@beckhoff.com>