rtc: davinci: enable compilation for omap architectures

The Davinci's onchip RTC is also present on TI OMAP1, AM33XX, AM43XX and
DRA7XX SOCs. So, let's enable compilation for these architectures too.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210602203805.11494-2-dariobin@libero.it