imx: add macro to detect whether USB PHY is active
This macro allows to detect whether the USB PHY is active. This
is helpful to detect if the boot ROM has previously started the
USB serial downloader.
The idea is taken from the mfgtool support in the NXP U-Boot:
http://git.freescale.com/git/cgit.cgi/imx/uboot-imx.git/commit/?h=imx_v2016.03_4.1.15_2.0.0_ga&id=
a352ed3c5184b95c4c9f7468f5fbb5f43de5e412
Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Eric Nelson <eric@nelint.com>
(cherry picked from commit
7d289d6239b29171bf9503869f1a92c084cf1c35)
