With this patch, it is possible to get the offset and size information
from the mtdpartiton setting in "mtdparts", similiar to the
"nand" commandos.

=> sf
sf - SPI flash sub-system

Usage:
sf probe [[bus:]cs] [hz] [mode] - init flash device on given SPI bus
                                  and chip select
sf read addr offset|partition len       - read `len' bytes starting at
                                          `offset' to memory at `addr'
sf write addr offset|partition len      - write `len' bytes from memory
                                          at `addr' to flash at `offset'
sf erase offset|partition [+]len        - erase `len' bytes from `offset'
                                          `+len' round up `len' to block size
sf update addr offset|partition len     - erase and write `len' bytes from memory
                                          at `addr' to flash at `offset'
=>
for example "env" is defined in mtdparts:

=> sf read 13000000 env
device 0 offset 0xd0000, size 0x10000
SF: 65536 bytes @ 0xd0000 Read: OK

zynq-uboot> mtdparts add nor0 0x10000@0x0 env
zynq-uboot> sf erase env 0x10000
SF: 65536 bytes @ 0x0 Erased: OK

zynq-uboot> sf write 0x100 env
device 0 offset 0x0, size 0x10000
SF: 65536 bytes @ 0x0 Written: OK

zynq-uboot> sf read 0x40000 env
device 0 offset 0x0, size 0x10000
SF: 65536 bytes @ 0x0 Read: OK

Signed-off-by: Heiko Schocher <hs@denx.de>
Tested-by: Jagannadh Teki <jteki@openedev.com>
Reviewed-by: Jagannadh Teki <jteki@openedev.com>