* arch: risc-v: Remove unused typedef for irqstate_t
NOTE: irqstate_t is defined in arch/risc-v/include/types.h
* arch: risc-v: Add typedef irqstate_t for __LP64__
* arch: risc-v: Add SMP support to K210 (RV64GC) processor
* boards: maxi-bit: Update READMEs and add smp/defconfig