arm: k3: Enable instruction cache for main domain SPL

Change spl_enable_dcache so it also enable icache on SPL
initialization for the main domain part of the boot flow. This
improves bootloader booting time.

Link: https://lore.kernel.org/all/20231109140958.1093235-1-joao.goncalves@toradex.com/


Signed-off-by: Joao Paulo Goncalves <joao.goncalves@toradex.com>
Tested-by: Nishanth Menon <nm@ti.com>