net: bcmasp: Divide init to allow partial bring up

net: bcmasp: Divide init to allow partial bring up

To prepare for a partial bring up of the interface during resume,
we break apart the bcmasp_netif_init() function into smaller chunks
that can be called as necessary. Also consolidate some functions that
do not need to be standalone.

Signed-off-by: Justin Chen <justin.chen@broadcom.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20260506213114.2002886-2-justin.chen@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>