firmware: qcom-scm: drop unneeded 'extern' specifiers

The 'extern' specifier in front of a function declaration has no effect.
Remove all of them from the qcom-scm header.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230913192826.36187-1-bartosz.golaszewski@linaro.org


Signed-off-by: Bjorn Andersson <andersson@kernel.org>