mmc: dw_mmc: Increase timeout to 4 minutes (as in Linux kernel)

mmc: dw_mmc: Increase timeout to 4 minutes (as in Linux kernel)

The commit: d9dbb97be0e4a550457aec5f11afefb446169c90
"mmc: dw_mmc: Zap endless timeout" removed endless loop waiting for end
of dw mmc transfer.

For some workloads - dfu test @ Odroid XU3 (sending 8MiB file) -
and SD cards (e.g. MicroSD Kingston 4GiB, Adata 4GiB)
the default timeout is to short.

The new value - 4 minutes (240 seconds) - is the same as the one used in
Linux kernel driver. Such fix should be good enough until we come up
with better fix for this issue.

Signed-off-by: Lukasz Majewski <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Pantelis Antoniou <[email protected]>
Cc: Tom Rini <[email protected]>
Tested-by: Przemyslaw Marczak <[email protected]>