In 8051 9 bit uart mode is used when communicating with multiple devices what is the provision for the same in lpc2148
No, that's not true.
The 9th bit in the 8051 "multiprocessor" mode (and other processors which support this) has a specific function to distinguish "address" from "data" bytes. And the 8052 Enhanced UART adds automatic hardware support for this.
True, you can instead use the 9th bit as a parity bit if you wish - but then you lose the "multiprocessor" functionality.
Again, this is a feature of the hardware and has nothing to do with any particular software toolset.
Oh, I used to take Automatic Address Recognition as an extension of basic 8051 architecture. I've checked Intel 80C51's datasheet and found it included in the 8051 core. With AAR feature it'll be much easier to implement multi-uC communication with reduced sw. overhead.
For LPC2148, of course it can implement AAR-like feature by PE interrupt and a few more lines of code.