kcmdlinectrl: define system property for kcmdlinectrl

This defines the kcmdline_prop context for properties controlled by
kcmdlinectrl, and defines a property called kcmdline.binder for
switching between the Rust and C implementations of the Binder driver.

It is intended that additional kcmdline properties introduced in the
future would share the same kcmdline_prop context.

Test: Verified that setprop/getprop work and that the value is loaded properly at boot
Bug: 326222756
Change-Id: Iea362df98d729ee110b6058c6e5fa6b6ace03d8e
diff --git a/private/file_contexts b/private/file_contexts
index e22a470..621e377 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -335,6 +335,7 @@
 /system/bin/perfetto        u:object_r:perfetto_exec:s0
 /system/bin/mtectrl         u:object_r:mtectrl_exec:s0
 /system/bin/misctrl         u:object_r:misctrl_exec:s0
+/system/bin/kcmdlinectrl         u:object_r:kcmdlinectrl_exec:s0
 /system/bin/traced        u:object_r:traced_exec:s0
 /system/bin/traced_perf        u:object_r:traced_perf_exec:s0
 /system/bin/traced_probes        u:object_r:traced_probes_exec:s0