Increase write buffer size in pflash emulation (Thomas Petazzoni).

Increase write buffer size in pflash emulation (Thomas Petazzoni).

The current flash emulation code advertises a write buffer size of 16
bytes (1 << 4, according to offset 0x2A of the CFI table). This is
very small compared to normal write buffer sizes, and makes the
process of writing to the flash very slow (at least from U-Boot).

This patch increases this size to 2048 bytes. Except the modification
of the CFI table, the only other required modification is to use
"value" instead of "cmd" to set pfl->counter, because cmd is truncated
to the 8 lower bits of value, while the number of bytes for a write
can now be greater than 255 bytes.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5454 c046a42c-6fe2-441c-8c8c-71466251a162