ARC: timer: rtc: implement read loop in "C" vs. inline asm

ARC: timer: rtc: implement read loop in "C" vs. inline asm

commit 922cc171998ac3dbe74d57011ef7ed57e9b0d7df upstream.

The current code doesn't even compile as somehow the inline assembly
can't see the register names defined as ARC_RTC_*
I'm pretty sure It worked when I first got it merged, but the tools were
definitely different then.

So better to write this in "C" anyways.

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>