In CPU definitions we should not be explicilty naming peripheral modules to use
via USEMODULE (one should use FEATURES_PROVIDED instead).
Plus add missing cpu_init() and periph_init() methods.
This commit removes periph_hwrng support from the pic32mx cpu builds as
pic32mx does not have hwrng only pic32mz does.
- removed ISR_STACKSIZE define where unused (set to 0)
- removed thread_arch_isr_stack_usage(), thread_arch_isr_stack_start(),
and/or thread_arch_isr_stack_pointer() where not implemented
