lib: sbi: move sbi_double_trap_handler() to a dedicated header

We will add new functions to sbi_double_trap.c in order to register an
SSE event, split this to a header as part of preparation work.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

include/sbi/sbi_trap_ldst.h

@@ -28,8 +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);
-
 ulong sbi_misaligned_tinst_fixup(ulong orig_tinst, ulong new_tinst,
 				 ulong addr_offset);