edd: add default mode CONFIG_EDD_OFF=n, override with edd={on,off}

Add a kernel parameter option to 'edd' to enable/disable BIOS Enhanced Disk
Drive Services.  CONFIG_EDD_OFF disables EDD while still compiling EDD into
the kernel.  Default behavior can be forced using 'edd=on' or 'edd=off' as
a kernel parameter.

[akpm@linux-foundation.org: fix kernel-parameters.txt]
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Matt Domsch <Matt_Domsch@dell.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>