block: support embedded device command line partition

block: support embedded device command line partition

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.

This code reference MTD partition, source "drivers/mtd/cmdlinepart.c"
About the partition verbose reference
"Documentation/block/cmdline-partition.txt"

[[email protected]: fix printk text]
[[email protected]: fix error return code in parse_parts()]
Signed-off-by: Cai Zhiyong <[email protected]>
Cc: Karel Zak <[email protected]>
Cc: "Wanglin (Albert)" <[email protected]>
Cc: Marius Groeger <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Brian Norris <[email protected]>
Cc: Artem Bityutskiy <[email protected]>
Signed-off-by: Wei Yongjun <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>