Change accessibility code to a timed dmtf signal instead of shortDtmfTone.

Only CDMA device RIL code supports sendBurstDtmfTone but the
accessibility code relied on that for sending dtmf tones. Add a 'timed
dtmf' function to perform a similar function without reliance on
burstDtmfTone code.

original CL adding this change: I85be84c5978d7580e58913ab0c8659a6a1ab7586
bug: 7553176

Change-Id: I1416e72bf497ce0706a0148606a44ad7c9445f5d
1 file changed