hvmloader: tidy pci_mem_{start,end}

hvmloader: tidy pci_mem_{start,end}

For one at least pci_mem_start has to be precisely 32 bits wide, so use
uint32_t for both. Otherwise expressions like "pci_mem_start <<= 1"
won't have the intended effect (in their context).

Further since its introduction pci_mem_end was never written to. Mark it
const to make this explicit.

Finally drop PCI_MEM_END: It is used just once and needlessly
disconnected from the other constant (RESERVED_MEMBASE) it needs to
match. Use RESERVED_MEMBASE as initializer of pci_mem_end instead.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>