sdhci: Add quirk for forcing maximum block size to 2048 bytes

FSL eSDHC controllers can support maximum block size up to 4096 bytes,
the MBL (Maximum Block Length) field in the capabilities register
extended by one bit, and is set to 0x3.

But the SDHCI core doesn't support blocks of 4096 bytes, and thus
forces blksz to the lowest value -- 512 bytes. With this patch we can
pin up the blksz to the maximum supported block size, i.e. 2048 bytes.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>