include: sbi_bitops: More useful bit operations

This patch extends our bit operation library with mechanism to:
1. Iteratively traverse bits
2. Set bit
3. Clear bit
4. Change bit
5. ... other helpful functions ...

Most the above is adopted from Xvisor sources.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

lib/sbi/objects.mk

@@ -12,6 +12,7 @@ libsbi-objs-y += riscv_atomic.o
 libsbi-objs-y += riscv_hardfp.o
 libsbi-objs-y += riscv_locks.o
 
+libsbi-objs-y += sbi_bitops.o
 libsbi-objs-y += sbi_console.o
 libsbi-objs-y += sbi_ecall.o
 libsbi-objs-y += sbi_ecall_base.o