OvmfPkg: use regular PCI bus enumeration for bhyve

[d-scott-phillips]

With the initial import of bhyve functionality, I set PcdPciDisableBusEnumeration = TRUE to follow the UDK2014.SP1 bhyve firmware's behavior of using the no-enumeration PCI Dxes from DuetPkg.

The enumeration disabled path is for Xen, which assumes that PCI devices are configured in the way that Xen configures them, and has various asserts to ensure this. Bhyve doesn't meet all the expectations of this code path, specifically that all 64-bit capable memory spaces are programmed at an address at or above 4G.

This prevents successfully booting with bhyve's nvme emulation, so here we switch to using the PCI enumeration path like QEMU.