Enable UART4 in AST2500

mw 1e6e2000 1688a8a8

mw 1e6e200c e1c47e80

mw 1e78f00c 93

mw 1e78f00c 27 //Baudrate 38400 (divisor =13x3=39=27h)

mw 1e78f00c 13

mw 1e78f000 45 //output 'D'