watchdog: tegra: rewrite on top of watchdog_core.c

watchdog: tegra: rewrite on top of watchdog_core.c

Get rid of all the miscdevice and ioctl handling, and reuse
what is provided by watchdog_core.c.

Reviewed-on: http://git-master/r/433779
(cherry picked from commit 6c82b3e80bf1df8586474132617f7ea02674b74b)

Change-Id: I682db9bd2e32268ce40d09e0a39495d43ed54b20
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Arun Kannan <akannan@nvidia.com>
Reviewed-on: http://git-master/r/454845
Reviewed-by: Mitch Luban <mluban@nvidia.com>
Tested-by: Mitch Luban <mluban@nvidia.com>
GVS: Gerrit_Virtual_Submit