lib: sbi: Add a simple external interrupt handling framework

Currently, the external interrupt handling is scattered between
sbi_init and sbi_trap. This patch moves all external interrupt
handling into a simple framework called sbi_irqchip.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>

lib/sbi/objects.mk

@@ -32,6 +32,7 @@ libsbi-objs-y += sbi_hsm.o
 libsbi-objs-y += sbi_illegal_insn.o
 libsbi-objs-y += sbi_init.o
 libsbi-objs-y += sbi_ipi.o
+libsbi-objs-y += sbi_irqchip.o
 libsbi-objs-y += sbi_misaligned_ldst.o
 libsbi-objs-y += sbi_platform.o
 libsbi-objs-y += sbi_pmu.o