soc: actions: include header to fix missing prototype

Include the header with prototype of owl_sps_set_pg to fix:

  drivers/soc/actions/owl-sps-helper.c:16:5: warning: no previous prototype for 'owl_sps_set_pg' [-Wmissing-prototypes]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>