BOOT: Add RAW ramdisk support to bootz

BOOT: Add RAW ramdisk support to bootz

This patch allows loading RAW ramdisk via bootz command. The raw ramdisk is
loaded only in case it's size is specified:

  bootz <kernel addr> <ramdisk addr>:<ramdisk size> <fdt addr>

For example:

  bootz 0x42000000 0x43000000:0x12345 0x44000000

Signed-off-by: Marek Vasut <[email protected]>
Signed-off-by: Rob Herring <[email protected]>
Cc: Tom Warren <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Simon Glass <[email protected]>
Cc: Stephen Warren <[email protected]>
Cc: Nicolas Pitre <[email protected]>
Cc: Wolfgang Denk <[email protected]>
Cc: Detlev Zundel <[email protected]>