bcm63xx: Enable endian check support for ath9k pci fixup.

Some ath9k caldatas need to be "endian checked".
This patch allows selecting wether to enable endian check or not.
Endian check is disabled by default.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@34105 3c298f89-4303-0410-b956-a3cf2f4a3e73