arm64: insn: Add support for encoding DSB

[ Upstream commit 63de8abd ]

To generate code in the eBPF epilogue that uses the DSB instruction,
insn.c needs a heler to encode the type and domain.

Re-use the crm encoding logic from the DMB instruction.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>