ptp_pch: Add dependency on HAS_IOMEM

On archs like S390 or um this driver cannot build nor work.
Make it depend on HAS_IOMEM to bypass build failures.

drivers/ptp/ptp_pch.c: In function ‘pch_remove’:
drivers/ptp/ptp_pch.c:571:3: error: implicit declaration of function ‘iounmap’ [-Werror=implicit-function-declaration]
drivers/ptp/ptp_pch.c: In function ‘pch_probe’:
drivers/ptp/ptp_pch.c:621:2: error: implicit declaration of function ‘ioremap’ [-Werror=implicit-function-declaration]

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: David S. Miller <davem@davemloft.net>