radio: iris: Increase the RT buffer to fit the RT header

Increase the RDS Radio text buffer size to fit the RT header.
And also limit the Radio text to maximum allowed length

Change-Id: Ib38b4bfaae83d5f381a831c2e202c7f3a52698b4
CRs-Fixed: 328036
Signed-off-by: Srinivasa Rao Uppala <uppalas@codeaurora.org>