acpi, acpi_piix, vt82c686: factor out PM_TMR logic

acpi, acpi_piix, vt82c686: factor out PM_TMR logic

factor out PM_TMR logic. Later This will be used by ich9 acpi.
Also fixes the same bug in vt82c686.c that was fixed by the following
commits.

> commit 055479feab63607b8042bb8ebb2e0523f17cbc4e
> Author: aliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162>
> Date:   Wed Jan 21 16:31:20 2009 +0000
>
>     Always return latest pmsts instead of the old one (Xiantao Zhang)
>
>     It may lead to the issue when booting windows guests with acpi=1
>     if return the old pmsts.
>
>     Signed-off-by: Xiantao Zhang <[email protected]>
>     Signed-off-by: Anthony Liguori <[email protected]>

Cc: Blue Swirl <[email protected]>
Cc: Huacai Chen <[email protected]>
Cc: Aurelien Jarno <[email protected]>
Signed-off-by: Isaku Yamahata <[email protected]>
Signed-off-by: Aurelien Jarno <[email protected]>