arm/arm64: arch_timer: Use archdata to indicate vdso suitability

Instead of comparing the name to a magic string, use archdata to
explicitly communicate whether the arch timer is suitable for
direct vdso access.

Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Scott Wood <oss@buserror.net>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/vdso.c

@@ -201,7 +201,7 @@ up_fail:
  */
 void update_vsyscall(struct timekeeper *tk)
 {
-	u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter");
+	u32 use_syscall = !tk->tkr_mono.clock->archdata.vdso_direct;
 
 	++vdso_data->tb_seq_count;
 	smp_wmb();