drm/amd/display: Turn global functions into static

Turn global functions that are only used locally into static ones. This
reduces the number of -Wmissing-prototypes warnings.
Signed-off-by: Arthur Grillo <arthurgrillo@riseup.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/irq/dcn201/irq_service_dcn201.c

@@ -37,7 +37,7 @@
 #include "soc15_hw_ip.h"
 #include "ivsrcid/dcn/irqsrcs_dcn_1_0.h"
 
-enum dc_irq_source to_dal_irq_source_dcn201(
+static enum dc_irq_source to_dal_irq_source_dcn201(
 		struct irq_service *irq_service,
 		uint32_t src_id,
 		uint32_t ext_id)