docs(ethos-n): update build-options.rst

Move documentation related to Arm(R) Ethos(TM)-N NPU driver from
docs/plat/arm/arm-build-options.rst to
docs/getting_started/build-options.rst.

Signed-off-by: Rajasekaran Kalidoss <rajasekaran.kalidoss@arm.com>
Change-Id: I388e8dcd3950b11bc3305f5e6396ee2e49c04493
3 files changed