[Feature][ZXW-96]uart 1and2 supports the maximum baudrate of 4M

Only Configure:No;
Affected branch:master;
Affected module:Uart;
Is it affected on both ZXIC and MTK: only ZXIC;
Self-test: Yes;
Doc Update:No

Change-Id: I48aacbadd9f69aa0f562bee515e91e8ed0999fdb
2 files changed