hw/timer/slavio_timer: Allow 64-bit accesses

Per the "NCR89C105 Chip Specification" referenced in the header:

                  Chip-level Address Map

  ------------------------------------------------------------------
  | 1D0 0000 ->   | Counter/Timers                        | W,D    |
  |   1DF FFFF    |                                       |        |
  ...

  The address map indicated the allowed accesses at each address.
  [...] W indicates a word access, and D indicates a double-word
  access.

The SLAVIO timer controller is implemented expecting 32-bit accesses.
Commit a3d12d073e restricted the memory accesses to 32-bit, while
the device allows 64-bit accesses.

This was not an issue until commit 5d971f9e67 which reverted
("memory: accept mismatching sizes in memory_region_access_valid").

Fix by renaming .valid MemoryRegionOps as .impl, and add the valid
access range (W -> 4, D -> 8).

Since commit 21786c7e59 ("memory: Log invalid memory accesses")
this class of bug can be quickly debugged displaying 'guest_errors'
accesses, as:

  $ qemu-system-sparc -M SS-20 -m 256 -bios ss20_v2.25_rom -serial stdio -d guest_errors

  Power-ON Reset
  Invalid access at addr 0x0, size 8, region 'timer-1', reason: invalid size (min:4 max:4)

  $ qemu-system-sparc -M SS-20 -m 256 -bios ss20_v2.25_rom -monitor stdio -S
  (qemu) info mtree
  address-space: memory
    0000000000000000-ffffffffffffffff (prio 0, i/o): system
      ...
      0000000ff1300000-0000000ff130000f (prio 0, i/o): timer-1
             ^^^^^^^^^                                 ^^^^^^^
                   \ memory region base address and name /

  (qemu) info qtree
  bus: main-system-bus
    dev: slavio_timer, id ""              <-- device type name
      gpio-out "sysbus-irq" 17
      num_cpus = 1 (0x1)
      mmio 0000000ff1310000/0000000000000014
      mmio 0000000ff1300000/0000000000000010 <--- base address
      mmio 0000000ff1301000/0000000000000010
      mmio 0000000ff1302000/0000000000000010
      ...

Reported-by: Yap KV <yapkv@yahoo.com>
Buglink: https://bugs.launchpad.net/bugs/1906905
Fixes: a3d12d073e ("slavio_timer: convert to memory API")
CC: qemu-stable@nongnu.org
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20201205150903.3062711-1-f4bug@amsat.org>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>

hw/timer/slavio_timer.c

@@ -331,6 +331,10 @@ static const MemoryRegionOps slavio_timer_mem_ops = {
     .write = slavio_timer_mem_writel,
     .endianness = DEVICE_NATIVE_ENDIAN,
     .valid = {
+        .min_access_size = 4,
+        .max_access_size = 8,
+    },
+    .impl = {
         .min_access_size = 4,
         .max_access_size = 4,
     },