soc: brcmstb: Split initialization

We may need access to family_id and product_id fairly early on boot for
other parts of the code (e.g: biuctrl.c), so split the initialization
between an early_init() and an arch_initcall() which allows us to do
that.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>