fs: fat: fix bug when write size is less than a sector size
arm: at91: enable mci support for at91sam9g20ek.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
arm: at91: add at91sam9g20ek_mmc_config, which can save environment in mmc card

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>