board: colibri_imx7: fix emmc detection

board: colibri_imx7: fix emmc detection

Later versions of Colibri iMX7D V1.1B modules use a "new" SoC fusing. The
difference lies in whether we enable the boot ROM to use the eMMC reset
signal. Depending on the SoC fuse, the boot ROM configures this pin as a
GPIO output to drive the reset signal. Our eMMC vs NAND detection
currently only sets that signal to a GPIO without explicitly setting any
direction. Previously, by default, it was set as an input. As the boot ROM
now configures it as an output, we receive a value of zero instead of one,
indicating the absence of the pull-up on eMMC modules.

To fix this, set the SION bit, allowing the reading back of the value
even if it is configured as an output by the boot ROM. It's important to
note that with the new SoC fusing, we now read back what the boot ROM
drives rather than the real value caused by the pull-up resistor. However,
if it were ever driven low, the eMMC would permanently be reset.

In addition, remove hard-coded variant in the eMMC build case as since the
commit 0c39564d0281 ("toradex: colibri_imx7: Enable nand/emmc detection
and set boot variant") will anyways always get overridden by the detection
routing in board code.

Fixes: 0c39564d ("toradex: colibri_imx7: Enable nand/emmc detection and set boot variant")
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Hiago De Franco <hiago.franco@toradex.com>