lib: sbi: add Ssdbltrp ISA extension support

Add Ssdbltrp trap handler support for S-mode double trap handling. If
the trap is received while in VS-mode, then the trap is redirected to
S-mode. If caught while in HS-mode, then an error is returned to the top
trap handler which will panic.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>

include/sbi/sbi_trap_ldst.h

@@ -28,4 +28,6 @@ int sbi_load_access_handler(struct sbi_trap_context *tcntx);
 
 int sbi_store_access_handler(struct sbi_trap_context *tcntx);
 
+int sbi_double_trap_handler(struct sbi_trap_context *tcntx);
+
 #endif