pwm: renesas-tpu: 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/built-in.o: In function `tpu_probe':
drivers/pwm/pwm-renesas-tpu.c:421: undefined reference to `devm_ioremap_resource'

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>