arm64: barriers: allow dsb macro to take option parameter

The dsb instruction takes an option specifying both the target access
types and shareability domain.

This patch allows such an option to be passed to the dsb macro,
resulting in potentially more efficient code. Currently the option is
ignored until all callers are updated (unlike ARM, the option is
mandated by the assembler).

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>