ar71xx: rework patch for qca953x/956x

ar71xx: rework patch for qca953x/956x

Patch cherry-picked from the following location:
https://www.codeaurora.org/cgit/quic/qsdk/oss/system/openwrt/commit/?h=release/coconut_ioe4531_2.0&id=5c357bf6c763e4140dddcc9a3bc5f005525a9c0e

Changelist,
    - add more register defines
    - add EHCI support
    - fix GPIO pin count to 18
    - fix chained irq disabled
    - fix GMAC0/GMAC1 initial
    - fix WMAC irq number to 47
    - merge the changes of dev-eth.c from the patch to file.

Signed-off-by: Miaoqing Pan <miaoqing@codeaurora.org>
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Backport of r46207

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@48854 3c298f89-4303-0410-b956-a3cf2f4a3e73