Sergey reported that some much older Dell systems don't support
the OEM string "Dell System" but instead supported www.dell.com
in OEM strings.

Match both of these to indicate that this driver is running on
a Dell system.

Reported-by: Sergey Kubushyn <ksi@koi8.net>
Tested-by: Sergey Kubushyn <ksi@koi8.net>
Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
[dvhart: Simplify DMI logic and eliminate unnecessary variables]
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>