west.yml: Make nxp hal a zephyr_library

Stops leaking long source paths in build directories and makes them
deterministic.

When building samples/hello_world for frdm_k64f, this changes the build
directories from:

build
└── zephyr
└── CMakeFiles
    └── zephyr.dir
	└── home
	    └── maureen
		└── zephyrproject
		    └── modules
			└── hal
			    └── nxp
				└── mcux
				    ├── devices
				    │   └── MK64F12
				    │       └── fsl_clock.c.obj
				    └── drivers
					└── kinetis
					    └── fsl_uart.c.obj

to:

build/
└── modules
└── nxp
    └── lib..__modules__hal__nxp.a

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>