SurfaceFlinger: expose idle timer as device config

Add a device config for idle timer to allow setting it from
a device.mk file

Bug: 126270036
Test: flashall the build and observe idle timer value
Change-Id: Ic1af3fd20b497a52e9740d898754c0c9eeb223ef
diff --git a/services/surfaceflinger/SurfaceFlingerProperties.cpp b/services/surfaceflinger/SurfaceFlingerProperties.cpp
index cb9a6c0..875fca8 100644
--- a/services/surfaceflinger/SurfaceFlingerProperties.cpp
+++ b/services/surfaceflinger/SurfaceFlingerProperties.cpp
@@ -209,6 +209,14 @@
     return static_cast<int32_t>(defaultValue);
 }
 
+int32_t set_idle_timer_ms(int32_t defaultValue) {
+    auto temp = SurfaceFlingerProperties::set_idle_timer_ms();
+    if (temp.has_value()) {
+        return *temp;
+    }
+    return defaultValue;
+}
+
 #define DISPLAY_PRIMARY_SIZE 3
 
 constexpr float kSrgbRedX = 0.4123f;