configs: j721e_evm_a72: Disable K3_SYSTEM_CONTROLLER

The K3 System Controller driver is used for loading and starting
the System Firmware, and is used only on R5 SPL. It need not be
enabled and built for the A72 U-Boot and SPL, so disable it from
the j721e_evm_a72 defconfig.

While at this, also remove the unneeded CONFIG_SPL_REMOTEPROC and
CONFIG_CMD_REMOTEPROC as no remoteprocs are now loaded from A72 SPL.

Signed-off-by: Suman Anna <s-anna@ti.com>