Remove pci_bios_bigmem_addr; set pci_bios_mem_addr=0xe0000000

Remove pci_bios_bigmem_addr; set pci_bios_mem_addr=0xe0000000

This patch removes pci_bios_bigmem_addr, and it changes
pci_bios_mem_addr to start at 0xe0000000.

The pci_bios_bigmem_addr was removed from bochs.  Also, the current
code looks wrong as nothing stops an address given from
pci_bios_bigmem_addr from overlapping an address given from
pci_bios_mem_addr.

The change also moves pci_bios_mem_addr back to 0xe0000000 - both the
acpi and mtrr code use 0xe0000000.