Thanks to Robert C Nelson who replied my query on Beaglebone black community.
One of the configuration, MMC_BLOCK_MINORS [=8] was set to 8 which was preventing driver to create more than 8 device files. I changed number and i am able to see all the partitions and respective device files.
Location:
│ -> Device Drivers
│ -> MMC/SD/SDIO card support (MMC [=y])
│ -> MMC block device driver (MMC_BLOCK [=y])
Hope this helps some having same problem.