esdhc: Workaround for card can't be detected on T4240QDS

Card detection pin is ineffective on T4240QDS Rev1.0.
There are two cards can be connected to board.
1. eMMC card is built-in board, can not be removed. so
   For eMMC card it is always there.
2. Card detecting pin is functional for SDHC card in Rev2.0.

This workaround force sdhc driver scan and initialize the card
regardless of whether the card is inserted or not in case Rev1.0.

Signed-off-by: Haijun Zhang <Haijun.Zhang@freescale.com>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>
Reviewed-by: York Sun <yorksun@freescale.com>