I have tried to change the android system-partition size to 5GB from 1.2GB and reduced data-parition from 5GB to 1.2GB, so rebuild aosp with modified BoardConfig.mk
Then came to know that same has to be updated in gpt_both0.bin and successfully created same with modified partition info(removed few partition) for android and flashed the new gpt_both0.bin
fastboot flash partition gpt_both0.bin
Once I have rebooted the device, dragonboard is not detected by either fastboot/adb utility. So listed the usbdevices using lsusb command.
Dragonboard detected as
Bus 002 Device 119: ID 05c6:9008 Qualcomm, Inc. Gobi Wireless Modem (QDL mode)
Bus 002 Device 108: ID 18d1:d00d Google Inc.
After googling that came to know about qualcomm download mode. so please guide me to put my dragonboard back to normal mode.