soc: qcom: Rename msm watchdog to wdt core

In preparation to change the qcom watchdog to a new core
framework that future watchdog drivers will utilize, the name
of the file needs to be changed. Due to the number of changes
needed in the file we need to rename it to reflect its new purpose.

Change-Id: Iac6ad57fbc02866f6716a44d7bb4a62d97e4a810
Signed-off-by: Branden Bonaby <bbonaby@codeaurora.org>