configs: am65x_evm_a53: 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 A53 U-Boot and SPL, so disable it from
both the GP and HS AM65x A53 defconfigs.

While at this, also remove the unneeded CONFIG_SPL_REMOTEPROC and
CONFIG_CMD_REMOTEPROC as no remoteprocs are now loaded from A53 SPL.

Signed-off-by: Suman Anna <s-anna@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>