pwm: tegra: resource allocation through devm_*

Using the devm_* for memory region allocation and clock handler
request. As a result, there is no need to explicitly free them and
hence saving some code.

Change-Id: Id69d40bd44622105ea4f8a37426dd83a694adb8d
Signed-off-by: Kunal Agrawal <kunala@nvidia.com>
Reviewed-on: http://git-master/r/121581
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Laxman Dewangan <ldewangan@nvidia.com>