ehci: refactor pci quirk to use standard dmi_check_system method

In commit 3610ea53 (ehci: workaround for pci
quirk timeout on ExoPC), a workaround was added to skip the negociation for
the handoff of the EHCI controller.

Refactor the DMI detection code to use standard dmi_check_system function.

Signed-off-by: Anisse Astier <anisse@astier.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>