commands: spi: Fix spi read procedure ...

Buffer for RX is set incorrectly.

barebox@Phytec phyCORE-i.MX27:/  spi -r 128 -v
device config
    bus_num       = 0
    max_speed_hz  = 1000000
    chip_select   = 0
    mode          = 0x0
    bits_per_word = 8

wrote 0 bytes
00000000:
read 128 bytes
00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
00000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
00000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
unable to handle paging request at address 0x4dffd3d0
pc : [<a7f05ec4>]    lr : [<a7f05ebc>]
sp : a7fff890  ip : a7fff860  fp : a7f68820
r10: a6ffe9bc  r9 : 00000000  r8 : 00000001
r7 : a6ffe9ec  r6 : a6f00000  r5 : a6ffe9ec  r4 : a6ffe9e4
r3 : a6ffe9e4  r2 : a6ffe9e5  r1 : a6ffe9e4  r0 : 4dffd3cc
Flags: nZCv  IRQs off  FIQs off  Mode SVC_32
...

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

mem: add the swab (swap bytes) option to memory_display() ...

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

introduce spi command ...

usefull to debug spi

The command allow to read/write on a spi device

Usage: spi [OPTION] [data to write 0xXX]
write/read spi device.
  -b <bus_num>  spi bus number (default = 0)
  -r <count>    to read
  -c <cs>       chip select (default = 0)
  -m <mode>     spi mode (default = 0)
  -f <hz>       max_speed_hz (default = 1MHz)
  -w <bit>      bits_per_word (default = 8)
  -v            verbose

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>