shusky/vibrator: Disable PWLE by default

Set chirp.enabled prop to 0 by default so that it will not cause tests
to fail.
Change prop to persist from ro so that it can be enabled for testing.

Bug: 286921585
Test: Tried using idlcli composePwle before/after setting prop
Change-Id: I7c0cd3604ba22a82fc1431d3b914994a270e9267
Signed-off-by: Nathan Kulczak <nathankulczak@google.com>