configs: ls1012a: Increase CONFIG_SYS_MALLOC_LEN value

configs: ls1012a: Increase CONFIG_SYS_MALLOC_LEN value

Previous attempt to increase CONFIG_SYS_MALLOC_LEN was done in commit
c084a8edf4e2 ("configs: ls1012a: Increase CONFIG_SYS_MALLOC_LEN size")
which increased malloc memory to ~1M.

PFE firmware alone requires 3M of dynamic memory allocation and
therefore, increase the config value to a larger value i.e 5M. This size
should be enough as of now to accommodate further memory requirements.

Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>