Revert "hw/block/pflash_cfi02: Reduce I/O accesses to 16-bit"

This reverts commit 3ae0343d.

Stephen Checkoway noticed commit 3ae0343d is incorrect.
This commit state all parallel flashes are limited to 16-bit
accesses, however the x32 configuration exists in some models,
such the Cypress S29CL032J, which CFI Device Geometry Definition
announces:

  CFI ADDR     DATA
  0x28,0x29 = 0x0003 (x32-only asynchronous interface)

Guests should not be affected by the previous change, because
QEMU does not announce itself as x32 capable:

    /* Flash device interface (8 & 16 bits) */
    pfl->cfi_table[0x28] = 0x02;
    pfl->cfi_table[0x29] = 0x00;

Commit 3ae0343d does not restrict the bus to 16-bit accesses,
but restrict the implementation as 16-bit access max, so a guest
32-bit access will result in 2x 16-bit calls.

Now, we have 2 boards that register the flash device in 32-bit
access:

- PPC: taihu_405ep

  The CFI id matches the S29AL008J that is a 1MB in x16, while
  the code QEMU forces it to be 2MB, and checking Linux it expects
  a 4MB flash.

- ARM: Digic4

  While the comment says "Samsung K8P3215UQB 64M Bit (4Mx16)",
  this flash is 32Mb (2MB). Also note the CFI id does not match
  the comment.

To avoid unexpected side effect, we revert commit 3ae0343d,
and will clean the board code later.

Reported-by: Stephen Checkoway <stephen.checkoway@oberlin.edu>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>