clocksource, acpi_pm.c: put acpi_pm_read_slow() under CONFIG_PCI

acpi_pm_read_slow() is only used when CONFIG_PCI=y, so move the definition
inside the ifdef.

Otherwise this causes a "defined but not used" warning when building with
CONFIG_ACPI=y and CONFIG_PCI=n (that's not supported yet, but it could
be).

Signed-off-by: Bjorn Helgaas <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>
Cc: Dominik Brodowski <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Len Brown <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

drivers/clocksource/acpi_pm.c

···
 	return v2;
 }
 
-static cycle_t acpi_pm_read_slow(void)
-{
-	return (cycle_t)acpi_pm_read_verified();
-}
-
 static cycle_t acpi_pm_read(void)
 {
 	return (cycle_t)read_pmtmr();
···
 	return 1;
 }
 __setup("acpi_pm_good", acpi_pm_good_setup);
+
+static cycle_t acpi_pm_read_slow(void)
+{
+	return (cycle_t)acpi_pm_read_verified();
+}
 
 static inline void acpi_pm_need_workaround(void)
 {