uboot-imx

hummingboard: Remove mx6solo specific support

Hummingboard dual, dual-lite and solo are now supported via SPL mechanism.

Remove the previous hummingboard support, which does not use SPL and supported
only the solo variant.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Reviewed-by: Tom Rini <trini@konsulko.com>