hw/char/mchp_pfsoc_mmuart: Use a MemoryRegion container

hw/char/mchp_pfsoc_mmuart: Use a MemoryRegion container

Our device have 2 different I/O regions:
- a 16550 UART mapped for 32-bit accesses
- 13 extra registers

Instead of mapping each region on the main bus, introduce
a container, map the 2 devices regions on the container,
and map the container on the main bus.

Before:

  (qemu) info mtree
    ...
    0000000020100000-000000002010001f (prio 0, i/o): serial
    0000000020100020-000000002010101f (prio 0, i/o): mchp.pfsoc.mmuart
    0000000020102000-000000002010201f (prio 0, i/o): serial
    0000000020102020-000000002010301f (prio 0, i/o): mchp.pfsoc.mmuart
    0000000020104000-000000002010401f (prio 0, i/o): serial
    0000000020104020-000000002010501f (prio 0, i/o): mchp.pfsoc.mmuart
    0000000020106000-000000002010601f (prio 0, i/o): serial
    0000000020106020-000000002010701f (prio 0, i/o): mchp.pfsoc.mmuart

After:

  (qemu) info mtree
    ...
    0000000020100000-0000000020100fff (prio 0, i/o): mchp.pfsoc.mmuart
      0000000020100000-000000002010001f (prio 0, i/o): serial
      0000000020100020-0000000020100fff (prio 0, i/o): mchp.pfsoc.mmuart.regs
    0000000020102000-0000000020102fff (prio 0, i/o): mchp.pfsoc.mmuart
      0000000020102000-000000002010201f (prio 0, i/o): serial
      0000000020102020-0000000020102fff (prio 0, i/o): mchp.pfsoc.mmuart.regs
    0000000020104000-0000000020104fff (prio 0, i/o): mchp.pfsoc.mmuart
      0000000020104000-000000002010401f (prio 0, i/o): serial
      0000000020104020-0000000020104fff (prio 0, i/o): mchp.pfsoc.mmuart.regs
    0000000020106000-0000000020106fff (prio 0, i/o): mchp.pfsoc.mmuart
      0000000020106000-000000002010601f (prio 0, i/o): serial
      0000000020106020-0000000020106fff (prio 0, i/o): mchp.pfsoc.mmuart.regs

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Tested-by: Bin Meng <bin.meng@windriver.com>
Message-id: 20210925133407.1259392-3-f4bug@amsat.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>