MIPS: Rename JZRISC to XBURST

The real name of the CPU present in the JZ line of SoCs from Ingenic is
XBurst, not JZRISC.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
[paul.burton@mips.com: Leave /proc/cpuinfo string as-is.]
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: od@zcrc.me
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org