PCI: endpoint: Fix pci_epf_alloc_space() to set correct MEM TYPE flags

pci_epf_alloc_space() sets the MEM TYPE flags to indicate a 32-bit
Base Address Register irrespective of the size. Fix it here to indicate
64-bit BAR if the size is > 2GB.

Tested-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>