mmc: sdhci-esdhc-imx: Enable ADMA2

Eanble the ADMA2 mode for freescale esdhc imx driver, tested on MX25
3DS board, MX51 BBG board and MX53 LOCO board.

This patch is only used to enable the ADMA2 for MX51/53 platforms.
MX25/35 can't support the ADMA2 mode, set BROKEN_ADMA quirk on
MX25/35 platforms.

The ADMA mode supported or not can be distinguished by bit 20 of
the Capability Register (offset 0x40) in the FSL eSDHC module.

Signed-off-by: Richard Zhu <richard.zhu@linaro.org>
Tested-and-acked-by: Eric Miao <eric.miao@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>