Hi Sankar,
There has been an update on this from the factory team. The following should be performed in sequence to activate A27 as an address line:
//FIX for the GPMC 16bit Multiplexed mode for 256MB access using the GPMC_A27 pin
WR_MEM_32(GPMC_CONFIG1_0,0x00000000); //Reset the Mux Mode
temp = RD_MEM_32(0x10000000); //Access the GPMC Memory to release the GPMC_A27 pin
WR_MEM_32(GPMC_CONFIG1_0,0x00001210); //16 bit, Multiplexed mode
The above is based on a GEL file, but the same sequence should be performed during GPMC initialization in Linux. GPMC_A11 should be pinmuxed to mode 4.