watchdog: sirfsoc: Add missing dependency on HAS_IOMEM

watchdog: sirfsoc: Add missing dependency on HAS_IOMEM

If HAS_IOMEM is not defined and SIRFSOC_WATCHDOG is enabled,
the build fails with the following error.

drivers/watchdog/sirfsoc_wdt.o: in function `sirfsoc_wdt_probe':
sirfsoc_wdt.c:(.text+0x112):
	undefined reference to `devm_platform_ioremap_resource'

Reported-by: Necip Fazil Yildiran <fazilyildiran@gmail.com>
Fixes: da2a68b3eb47 ("watchdog: Enable COMPILE_TEST where possible")
Link: https://lore.kernel.org/r/20201108162550.27660-2-linux@roeck-us.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>