MIPS: cpu-probe: Mark XBurst CPU as having vtagged caches

XBurst CPUs present in Ingenic SoCs have virtually tagged caches,
according to the <cpu-features-override.h> header.

Add that information to cpu_probe_ingenic().

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>