watchdog: omap_wdt: Switch required include for watchdog defines

All of the required values for using the omap_wdt.c driver are found in
<asm/ti-common/omap_wdt.h> and this is what is indirectly pulled in via
<asm/arch/hardware.h> when it exists.

Signed-off-by: Tom Rini <trini@konsulko.com>