Make init.userspace_reboot.is_supported a rw property

General recommendation is to avoid read-only properties, and instead control
"read-onlines" by only allowing init/vendor_init to set the property.

Since ro.init.userspace_reboot.is_supported was added in this release, and
nobody outside of the platform is querying it directly, it should be fine to
simply rename it.

Test: adb shell getprop init.userspace_reboot.is_supported
Test: atest CtsUserspaceRebootHostSideTestCases
Bug: 152803929
Change-Id: Ie3604b315a5d2a846037064ad9a29258f2cad9d0
Merged-In: Ie3604b315a5d2a846037064ad9a29258f2cad9d0
(cherry picked from commit bb9699c2e10e707a2585b33271f83db8bced2d04)
diff --git a/target/product/userspace_reboot.mk b/target/product/userspace_reboot.mk
index 76ec83d..3f881af 100644
--- a/target/product/userspace_reboot.mk
+++ b/target/product/userspace_reboot.mk
@@ -16,6 +16,4 @@
 
 # Inherit this when the target supports userspace reboot
 
-PRODUCT_PROPERTY_OVERRIDES := ro.init.userspace_reboot.is_supported=true
-
-# TODO(b/135984674): configure userspace reboot related properties
+PRODUCT_PROPERTY_OVERRIDES := init.userspace_reboot.is_supported=true