Changing the number of MMC_BLOCK_MINORS to 16 from 8. To allow for more partitions.

Number of minors per block device. One is needed for every
partition on the disk (plus one for the whole disk).

Number of total MMC minors available is 256, so your number
of supported block devices will be limited to 256 divided
by this number.

Default is 8 to be backwards compatible with previous
hardwired device numbering.