mtd: gpmi: only scan two chips for imx6
mtd: gpmi: only scan two chips for imx6

We cannot scan two chips for imx23 and imx28:
  imx23: the Ready-Busy1 line is not connected for some board.
  imx28: we do not set the pinctrl for Ready-Busy1

So we only scan two chips for imx6.

Signed-off-by: Huang Shijie <3c7352d1cf9fbb1bd8706c56d582c0ade3f5dabf@freescale.com>
Signed-off-by: Brian Norris <ac73eed4b8a8c9127255a2696c52b2e7503720b8@gmail.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs