ext: hal: Add MSP432P4XX SDK Kconfig/Build support

This patch adds Kconfig/build support to MSP432P4XX
SDK. MSP432P4XX microcontrollers have driverlib flashed
onto the ROM, which will be used by default.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>