Input: Gate setKernelWakeEnabled with a flag

This flag was previously added but not used.

Bug: 372812925
Change-Id: If6ebb8b73b3dbe802d7fd3dac0ac689000102014
Test: Plug in USB mouse and power/wakeup is not changed without
      explicitly setting this flag "enabled".
Flag: com.android.input.flags.set_input_device_kernel_wake