This is more in line with the actual hardware (u32 registers), and will still
work if PRIMASK or FAULTMASK ever have more than 1 bit defined.
The functions cm_is_masked_interrupts() and cm_is_masked_faults() are
unchanged, since returning 'bool' fits with the function naming.
Fixes most of github issue #475. What remains "unfixed" is the absence
of functions to simply 'get' the u32 value of PRIMASK and FAULTMASK registers.
1d36685759