pinctrl-msm: Allow the driver to be compiled as a module

Currently, the Kconfig state of MSM_PINCTRL is declared as 'bool',
thus not allowing the driver to be compiled as a module. Hence,
change it to 'tristate' so that the driver can be compiled as a
dynamically loadable kernel module.

Also add MODULE_LICENSE to the driver.

Change-Id: Ica74f8c1ebccaf7eff7e25cb53bb2be759596e8a
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>