rtc: s3c: define s3c_rtc structure to remove global variables.

Define s3c_rtc structure including necessary variables for S3C RTC device
instead of global variables.  This patch improves the readability by
removing global variables.

Signed-off-by: Chanwoo Choi <[email protected]>
Acked-by: Kyungmin Park <[email protected]>
Cc: Alessandro Zummo <[email protected]>
Cc: Kukjin Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>