Embedded device command line partition
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Read block device partition table from command line.
The partition used for fixed block device (eMMC) embedded device.
It is no MBR, save storage space. Bootloader can be easily accessed
by absolute address of data on the block device.
Users can easily change the partition.

The format for the command line is just like mtdparts:

blkdevparts=<blkdev-def>[;<blkdev-def>]
  <blkdev-def> := <blkdev-id>:<partdef>[,<partdef>]
    <partdef> := <size>[@<offset>](part-name)

<blkdev-id>
    block device disk name, embedded device used fixed block device,
    it's disk name also fixed. such as: mmcblk0, mmcblk1, mmcblk0boot0.

<size>
    partition size, in bytes, such as: 512, 1m, 1G.

<offset>
    partition start address, in bytes.

(part-name)
    partition name, kernel send uevent with "PARTNAME". application can create
    a link to block device partition with the name "PARTNAME".
    user space application can access partition by partition name.

Example:
    eMMC disk name is "mmcblk0" and "mmcblk0boot0"

  bootargs:
    'blkdevparts=mmcblk0:1G(data0),1G(data1),-;mmcblk0boot0:1m(boot),-(kernel)'

  dmesg:
    mmcblk0: p1(data0) p2(data1) p3()
    mmcblk0boot0: p1(boot) p2(kernel)
