watchdog: OMAP: use standard GETBOOTSTATUS interface; use platform_data fn ptr

watchdog: OMAP: use standard GETBOOTSTATUS interface; use platform_data fn ptr

Previously the OMAP watchdog driver used a non-standard way to report
the chip reset source via the GETBOOTSTATUS ioctl.  This patch
converts the driver to use the standard WDIOF_* flags for this
purpose.

This patch may break existing userspace code that uses the existing
non-standard data format returned by the OMAP watchdog driver's
GETBOOTSTATUS ioctl.  To fetch detailed reset source information,
userspace code will need to retrieve it directly from the CGRM or PRM
drivers when those are completed.

Previously, to fetch the reset source, the driver either read a
register outside the watchdog IP block (OMAP1), or called a function
exported directly from arch/arm/mach-omap2.  Both approaches are
broken.  This patch also converts the driver to use a platform_data
function pointer.  This approach is temporary, and is due to the lack
of drivers for the OMAP16xx+ Clock Generation and Reset Management IP
block and the OMAP2+ Power and Reset Management IP block.  Once
drivers are available for those IP blocks, the watchdog driver can be
converted to call exported functions from those drivers directly.
At that point, the platform_data function pointer can be removed.

In the short term, this patch is needed to allow the PRM code to be
removed from arch/arm/mach-omap2 (it is being moved to a driver).

This version integrates a fix from Jon Hunter <jon-hunter@ti.com>
that avoids a NULL pointer dereference in a DT-only boot, and integrates
a patch commit message fix from Felipe Balbi <balbi@ti.com>.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Wim Van Sebroeck <wim@iguana.be>
Acked-by: Wim Van Sebroeck <wim@iguana.be>
[paul@pwsan.com: integrated pdata fix from Jon Hunter]
Cc: Jon Hunter <jon-hunter@ti.com>
[paul@pwsan.com: integrated changelog fix from Felipe Balbi]
Cc: Felipe Balbi <balbi@ti.com>