efi_loader: AllocateAddress requires page address

AllocatePages() can be called with Type=AllocateAddress. Such a call can
only succeed if *Memory points to the address of an unallocated page range.

A call with *Memory being an address that is not page aligned must not
succeed. The UEFI specification requires returning EFI_OUT_OF_RESOURCES
if the requested pages cannot be allocated.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>