arm: Clear primask and faultmask during startup

A bootloader may leave primask or faultmask set, so clear them during
startup when we enable interrupts and switch to the main thread.
Previously we only cleared primask for architecture variants which don't
support basepri, but now we do it for all architecture variants.

Fixes a failure on mimxrt1050_evk with the latency_measure test and
shell_module sample when using an nxp internal bootloader.

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