configs: j721e_evm_r5_defconfig: Increase early malloc size

Increase R5 SPL early malloc memory pool by ~7K to accommodate SPL USB
DFU boot requirements

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>