xen/gnttab: Use phys_addr_t to describe the grant frame base address

xen/gnttab: Use phys_addr_t to describe the grant frame base address

On ARM, address size can be 32 bits or 64 bits (if CONFIG_ARCH_PHYS_ADDR_T_64BIT
is enabled).
We can't assume that the grant frame base address will always fits in an
unsigned long. Use phys_addr_t instead of unsigned long as argument for
gnttab_setup_auto_xlat_frames.

Signed-off-by: Julien Grall <[email protected]>
Signed-off-by: Stefano Stabellini <[email protected]>
Acked-by: Ian Campbell <[email protected]>
Reviewed-by: David Vrabel <[email protected]>