am335x_evm: Remove SPI SPL from NOR support target

am335x_evm: Remove SPI SPL from NOR support target

When using the am335x_evm_nor target one is generally expecting to be
used in an environment when you want to program the NOR and not a
"deployment" type target.  In addition this only supports the Beaglebone
White with the memory cape and NOR module installed, which precludes the
presence of SPI flash.  Drop SPI as we were getting close to the binary
limit in some cases and slightly over with other toolchains.

Signed-off-by: Tom Rini <trini@ti.com>