soc: ti: k3: am6x: Fix AM62X M4 RAT initialisation

Commit b73c5578 ("soc: ti: move init code from SYS_INIT to hooks")
changed SYS_INIT to init hooks. For AM6x M4 target soc_prep_hook()
was added by mistake instead of soc_early_init_hook(), the platform needs
RAT translation initialized before any other operation and the platform
failed to boot with this change, fix this by replacing with
soc_early_init_hook()

Signed-off-by: Vaishnav Achath <vaishnav.a@ti.com>