west.yml: Make openisa hal a zephyr_library

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

When building samples/hello_world for rv32m1_vega_ri5cy, this changes
the build directories from:

build/
└── zephyr
└── CMakeFiles
    └── zephyr.dir
	└── home
	    └── maureen
		└── zephyrproject
		    └── modules
			└── hal
			    └── openisa
				└── vega_sdk_riscv
				    └── devices
					└── RV32M1
					    └── drivers
						├── fsl_clock.c.obj
						└── fsl_lpuart.c.obj
to:

build/
└── modules
└── openisa
    └── lib..__modules__hal__openisa.a

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