arm: am335x-pdu001: Remove SPI support

On this board SPI is only used to configure the SoC driving the LC TFT
display which is not used in U-Boot. Hence remove SPI support.
Signed-off-by: NFelix Brack <fb@ltec.ch>

configs/am335x_pdu001_defconfig

@@ -50,6 +50,5 @@ CONFIG_SPL_DM_REGULATOR=y
 CONFIG_DM_REGULATOR_FIXED=y
 CONFIG_DM_REGULATOR_TPS65910=y
 CONFIG_CONS_INDEX=4
-CONFIG_SPI=y
 # CONFIG_USE_TINY_PRINTF is not set
 # CONFIG_EFI_LOADER is not set