arch: arm: aarch32: rename z_arm_int_lib_init() function

We rename the z_arm_int_lib_init() function to
z_arm_interrupt_init(), aligning to how other
ARCHes name their IRQ initialization function.
There is nothing about 'library' in this
functionality, so we remove the 'lib' in-fix.

The commit does not introduce any behavior changes.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>