clocksource/drivers/mips-gic-timer: Only use VDSO_CLOCKMODE_GIC when it is a available

VDSO_CLOCKMODE_GIC is only defined if CONFIG_GENERIC_GETTIMEOFDAY is
enabled. Right now this is always the case, but it will change soon.

Prepare for the potential unavailability of VDSO_CLOCKMODE_GIC.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Link: https://patch.msgid.link/20260521-vdso-mips-kconfig-v1-6-2f79dcd6c78f@linutronix.de

drivers/clocksource/mips-gic-timer.c

@@ -198,7 +198,9 @@ static struct clocksource gic_clocksource = {
 	.name			= "GIC",
 	.read			= gic_hpt_read,
 	.flags			= CLOCK_SOURCE_IS_CONTINUOUS,
+#ifdef CONFIG_GENERIC_GETTIMEOFDAY
 	.vdso_clock_mode	= VDSO_CLOCKMODE_GIC,
+#endif
 };
 
 static void gic_clocksource_unstable(char *reason)