The ARM security extensions introduced the smc instruction, which is not
supported by all versions of GAS.

This patch introduces opcodes-sec.h, so that smc is made available in a
similar manner to hvc.
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NDave Martin <dave.martin@linaro.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>