x86: Force HPET readback_cmp for all ATI chipsets

commit 30a564be (x86, hpet: Restrict read back to affected ATI
chipset) restricted the workaround for the HPET bug to SMX00
chipsets. This was reasonable as those were the only ones against
which we ever got a bug report.

Stephan Wolf reported now that this patch breaks his IXP400 based
machine. Though it's confirmed to work on other IXP400 based systems.

To error out on the safe side, we force the HPET readback workaround
for all ATI SMbus class chipsets.

Reported-by: Stephan Wolf <stephan@letzte-bankreihe.de>
LKML-Reference: <alpine.LFD.2.00.1007142134140.3321@localhost.localdomain>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Stephan Wolf <stephan@letzte-bankreihe.de>
Acked-by: Borislav Petkov <borislav.petkov@amd.com>