This commit removes the riscv_interrupts.h header is it has become redundant. The previously
exposed API has been handled as follows:
- "riscv_interrupt_enable()" and "riscv_interrupt_disable()" have been removed. These functions
were declarations only and never had any implementation.
- "riscv_global_interrupts_enable()" and "riscv_global_interrupts_disable()" renamed to
"rv_utils_intr_global_enable()" and "rv_utils_intr_global_disable()" respectively and now
placed in rv_utils.h
