powerpc/pseries: include linux/types.h in asm/hvcall.h

Commit 6e032b35 ("powerpc/powernv: Check device-tree for RFI flush
settings") uses u64 in asm/hvcall.h without including linux/types.h

This breaks hvcall.h users that do not include the header themselves.

Fixes: 6e032b35

 ("powerpc/powernv: Check device-tree for RFI flush settings")
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>