configs: am62x_evm_r5: Increase size of malloc_simple heap after relocation

On AM62x SK we can see a boot failure with signature "alloc space
exhausted", so fix by increasing size of SPL_STACK_R_MALLOC_SIMPLE_LEN.

Fixes: 128f8129 ("arm: dts: k3: binman: am625: add support for signing TIFSSTUB Images")
Signed-off-by: Judith Mendez <jm@ti.com>
Tested-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Reviewed-by: Bryan Brattlof <bb@ti.com>