ip17xx: Introduce indirection of low-level operations

ip17xx: Introduce indirection of low-level operations

This patch introduces seperation between low-level and high-level parts
of the driver. The low-level functions are now called via pointers stored
in struct ip175c_regs.

The only functional changes are:

  o  correct_vlan_state() is now called as a part of every update_state().

  o  The order of setting of MODE_REG and resetting switch ports
     has changed. (These are independent actions, so it should not matter.)

  o  ip175c_set_tagged() sets the tags via update_state() instead of writing
     directly to the registers.

  o  The same for ip175c_set_pvid().

The only gaps in this abstraction are operations on ports (get_port_speed
and friends), which access PHY registers directly.

Signed-off-by: Martin Mares <mj@ucw.cz>
Signed-off-by: Patrick Horn <patrick.horn@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@21714 3c298f89-4303-0410-b956-a3cf2f4a3e73