MIPS: CPS: Read GIC_VL_IDENT directly, not via irqchip driver

Rather than calling the gic_read_local_vp_id() function from the GIC
irqchip driver, call read_gic_vl_ident() to read the GIC_VL_IDENT
register directly. This will allow us to remove gic_read_local_vp_id()
from the irqchip driver in a further patch, since that driver doesn't
actually care about the register's value.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17023/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>