imx: Move some i.MX common functions into the imx-common directory

imx: Move some i.MX common functions into the imx-common directory

This patch moves the following functions into the imx-common
directory:

- mxs_wait_mask_set()
- mxs_wait_mask_clr()
- mxs_reset_block()

These are currently used by i.MX28. But the upcoming GPMI NAND port
for i.MX6 will also use these functions. So lets move them to a
common location to re-use them.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>