arm, davinci: move davinci_rtc struct to hardware.h

move struct davinci_rtc to arch/arm/include/asm/arch-davinci/hardware.h
and add RTC_KICK0R_WE, RTC_KICK1R_WE defines,
so they are global useable.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Sandeep Paulraj <s-paulraj@ti.com>