v3/ec: default the SD mux to the FPGA

When configuring the SD mux, set it to the FPGA so that we can boot
with a minimum number of commands.

BUG=None
TEST=Power on the chameleon. Run `fpga on` and then `uart` from the
shell (without the `sd fpga` or `fpga bootmode sdio` commands).
Observe that the FPGA boots up from the SD card.

Change-Id: I80521bc0ace95938753b2725579f07262ae25ecc
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/chameleon/+/3082647
Tested-by: Paul Fagerburg <[email protected]>
Commit-Queue: Paul Fagerburg <[email protected]>
Reviewed-by: Wai-Hong Tam <[email protected]>
Reviewed-by: Sam Hurst <[email protected]>
1 file changed