mmc: sdhci: Avoid commands errors by simple timeout adaptation.

Old command timeout value was too small and it caused I/O errors which
led to uncompleted read/write/erase operations and filesystem errors.
Timeout adaptation fixes this issue.

Changes in sdhci_send_command() function:
- change timeout variable to static
- increase default command timeout to 100 ms
- add definition of max command timeout value,
  which can be redefined in each board config file
- wait for card ready state for max defined time
  if it doesn't exceed defined maximum or return COMM_ERR

Once successfully increased timeout value will be used in next function
call. This fix was tested on Goni, Trats, Trats2 boards by testing UMS
on MMC storage.

Changes v2:
- move global variable cmd_timeout into function sdhci_send_command()
- change condition "==" to ">=" when comparing time with timeout
- print information about timeout increasing and card busy timeout

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>