net: mvpp2: handle register mapping and access for PPv2.2

This commit adjusts the mvpp2 driver register mapping and access logic
to support PPv2.2, to handle a number of differences.

Due to how the registers are laid out in memory, the Device Tree binding
for the "reg" property is different:

 - On PPv2.1, we had a first area for the packet processor
   registers (common to all ports), and then one area per port.

 - On PPv2.2, we have a first area for the packet processor
   registers (common to all ports), and a second area for numerous other
   registers, including a large number of per-port registers

In addition, on PPv2.2, the area for the common registers is split into
so-called "address spaces" of 64 KB each. They allow to access per-CPU
registers, where each CPU has its own copy of some registers. A few
other registers, which have a single copy, also need to be accessed from
those per-CPU windows if they are related to a per-CPU register. For
example:

  - Writing to MVPP2_TXQ_NUM_REG selects a TX queue. This register is a
    per-CPU register, it must be accessed from the current CPU register
    window.

  - Then a write to MVPP2_TXQ_PENDING_REG, MVPP2_TXQ_DESC_ADDR_REG (and
    a few others) will affect the TX queue that was selected by the
    write to MVPP2_TXQ_NUM_REG. It must be accessed from the same CPU
    window as the write to the TXQ_NUM_REG.

Therefore, the ->base member of 'struct mvpp2' is replaced with a
->cpu_base[] array, each entry pointing to a mapping of the per-CPU
area. Since PPv2.1 doesn't have this concept of per-CPU windows, all
entries in ->cpu_base[] point to the same io-remapped area.

The existing mvpp2_read() and mvpp2_write() accessors use cpu_base[0],
they are used for registers for which the CPU window doesn't matter.

mvpp2_percpu_read() and mvpp2_percpu_write() are new accessors added to
access the registers for which the CPU window does matter, which is why
they take a "cpu" as argument.

The driver is then changed to use mvpp2_percpu_read() and
mvpp2_percpu_write() where it matters.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>