mmc: sdhci: Use timer based timeout detection in sdhci_send_command()

The loop counter based timeout detection does not work on the Armada
38x based board (DB-88F6820-GP). At least with dcache enabled a
timeout is detected. Without dcache enabled, the timeout does not
occur. Increasing the loop counter solves this issue. But a better
solution is to use a timer based timeout detection instead. This
patch now implements this timer based detection.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>
Cc: Luka Perkov <luka.perkov@sartura.hr>