Enable AHCI in pcflop kernel configuration.

Since the installer doesn't need to be able to boot from
floppy anymore, I suggest to add the AHCI driver to
the installation kernel, so the CD would permit to install
Plan 9 on a wider range of machines.

Notes:
Sun Feb 23 02:30:24 EST 2014 geoff
    do we still need pcflop?  doesn't pccd replace it completely?
    ugh.


Reference: /n/sources/patch/pcflop-ahci
Date: Mon Feb 18 20:12:18 CET 2013
Signed-off-by: djc@9grid.fr
Reviewed-by: djc

--- /sys/src/9/pc/pcflop	Mon Feb 18 20:12:05 2013
+++ /sys/src/9/pc/pcflop	Mon Feb 18 20:12:01 2013
@@ -75,7 +75,7 @@
 	sdata		pci sdscsi
 	sd53c8xx	pci sdscsi
 	sdmylex		pci sdscsi
-#	sdiahci		pci sdscsi
+	sdiahci		pci sdscsi
 
 	uarti8250