Make the default value of flashlight availibility to true.

We read from SettingsProvider to decide whether flashlight slice is
available. However, when switching to the second user, FLASHLIGHT_AVAILABLE
will be null. The default was 0 which causes the slice returning null,
so we have to set it to 1 when there is a physical flash unit to be
consistent with system ui.

Fixes: 134734608
Test: robotest
Change-Id: I981461b1b66e6e273e13a9cbcba96e3ccf0aec68