arm: Remove flea3 board

This board has not been converted to CONFIG_DM by the deadline.
Remove it.  As this is the last mx35 platform, remove that support as
well.

Cc: Stefano Babic <sbabic@denx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by: Stefano Babic <sbabic@denx.de>