armv7R: K3: am654: Use full malloc in SPL both pre and post reloc

armv7R: K3: am654: Use full malloc in SPL both pre and post reloc

In order to be able to use things like file system drivers early on in
SPL (before relocation) in a memory-constrained environment when DDR is
not yet available we cannot use the simple malloc scheme which does not
implement the freeing of previously allocated memory blocks. To address
this issue go ahead and enable the use of the full malloc by manually
initializing the required functionality inside board_init_f by creating
a full malloc pool inside the pre-relocation malloc pool.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>