rtc: omap: kicker mechanism support

rtc: omap: kicker mechanism support

OMAP RTC IP can have kicker feature.  This prevents spurious writes to
register.  To write to registers kicker lock has to be released.
Procedure to do it as follows,

1. write to kick0 register, 0x83e70b13
2. write to kick1 register, 0x95a4f1e0

Writing value other than 0x83e70b13 to kick0 enables write locking, more
details about kicker mechanism can be found in section 20.3.3.5.3 of
AM335X TRM @www.ti.com/am335x

Here id table information is added and is used to distinguish those that
require kicker handling and the ones that doesn't need it.  There are more
features in the newer IP's compared to legacy ones other than kicker,
which driver currently doesn't handle, supporting additional features
would be easier with the addition of id table.

Older IP (of OMAP1) doesn't have revision register as per TRM, so revision
register can't be relied always to find features, hence id table is being
used.

While at it, replace __raw_writeb/__raw_readb with writeb/readb; this
driver is used on ARMv7 (AM335X SoC)

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Daniel Mack <zonque@gmail.com>
Cc: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>