firmware: arm_scmi: Extend perf protocol ops to get number of domains

[ Upstream commit e9090e70

 ]

Similar to other protocol ops, it's useful for an scmi module driver to get
the number of supported performance domains, hence let's make this
available by adding a new perf protocol callback. Note that, a user is
being added from subsequent changes.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20230825112633.236607-2-ulf.hansson@linaro.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Stable-dep-of: 8e3c98d9

 ("firmware: arm_scmi: Fix frequency truncation by promoting multiplier type")
Signed-off-by: Sasha Levin <sashal@kernel.org>