lib: sbi: add support for firmware features extension

This extension allows the software running in supervisor mode to control
the behavior of various features of the SBI [1]. Implement the support
for such extension.

Link: https://lists.riscv.org/g/tech-prs/message/924 [1]
Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

lib/sbi/objects.mk

@@ -65,6 +65,7 @@ libsbi-objs-y += sbi_domain_context.o
 libsbi-objs-y += sbi_domain.o
 libsbi-objs-y += sbi_emulate_csr.o
 libsbi-objs-y += sbi_fifo.o
+libsbi-objs-y += sbi_fwft.o
 libsbi-objs-y += sbi_hart.o
 libsbi-objs-y += sbi_heap.o
 libsbi-objs-y += sbi_math.o