qemu: Always assume support for QEMU_CAPS_PIIX_DISABLE_S* and QEMU_CAPS_ICH9_DISABLE_S*

qemu: Always assume support for QEMU_CAPS_PIIX_DISABLE_S* and QEMU_CAPS_ICH9_DISABLE_S*

The support for PIIX power management was added in qemu commit
v1.0-3094-g459ae5ea5a and the suport for ICH9 power management was added
in qemu commit v2.2.0-542-g6ac0d8d44c and both can't be compiled out.

This means we can always assume support for these features. Remove the
validation and impossible tests. Move relevant bits from
'q35-pm-disable' to 'q35' test case.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>