ARM: 7552/1: mmc: mmci: Switching off HWFC for SDIO depends on MCLK

For writes, HWFC shall be switched off when transfer size <= 8
bytes and when MCLK rate is above 50 MHz. For 50MHz and below
it shall be switched off when transfer size < 8 bytes.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Johan Rudholm <johan.rudholm@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>