ath9k: Register id table for platform device

Currently the device id in the platform driver is hardcoded to an id
which is specific to AR9130/AR9132 SOCs as it supports only wmac (wireless mac)
of these SOCs. But this needs to be dynamic when we want to support different
wmac of SOCs. So add id_table to driver to make it extendable to more SOCs.

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Acked-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>