Fix QEMU's write cache reporting

Make QEMU consistently report write caching support for emulated IDE drives to fix a hang during SLES 9 HVM guest installation.

Without this, the SLES 9 installer kernels (32 and 64 bit) were getting inconsistent information from QEMU as to whether the (emulated) IDE drives support write caching (which they do). So part of the kernel thought write caching was enabled (and enabled the usage of barrier writes) and part of it didn't, which triggered a bug in which the same barrier write is submitted over and over again ...

Fixed by setting another bit in the WIN_IDENTIFY (IDE drive "identify" command) response to indicate we really, truly support write caching.

diff -r 52d3aa322e0d tools/ioemu/hw/ide.c
@@ -687,7 +687,8 @@ static void ide_identify(IDEState *s)
     /* 13=flush_cache_ext,12=flush_cache,10=lba48 */
     put_le16(p + 83, (1 << 14) | (1 << 13) | (1 <<12) | (1 << 10));
     put_le16(p + 84, (1 << 14));
-    put_le16(p + 85, (1 << 14));
+    /* 14=nop 5=write_cache */
+    put_le16(p + 85, (1 << 14) | (1 << 5));
     /* 13=flush_cache_ext,12=flush_cache,10=lba48 */
     put_le16(p + 86, (1 << 14) | (1 << 13) | (1 <<12) | (1 << 10));
     put_le16(p + 87, (1 << 14));

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