kernel: add more dsa b53 pending patches
These patches have now received a positive review upstream, so let's add them
to pending patches.
776-net-dsa-b53-mmap-add-phy-ops.patch:
This is mostly bmips/bcm63xx-specific to get external switches working
without hanging the device when accessing certain registers.
777-net-dsa-b53-mdio-add-support-for-BCM53134:
This adds support for BCM53134 switch on DSA B53, so any target using DSA B53
can benefit from it.
Also fix sercomm-h500-s external switch IMP port phy-mode.
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>