MIPS: smp-cps: Pull boot config retrieval out of mips_cps_boot_vpes

MIPS: smp-cps: Pull boot config retrieval out of mips_cps_boot_vpes

The mips_cps_boot_vpes function previously included code to retrieve
pointers to the core & VPE boot configuration structs. These structures
were used both by mips_cps_boot_vpes and by its mips_cps_core_entry
callsite. In preparation for skipping the call to mips_cps_boot_vpes on
some invocations of mips_cps_core_entry, pull the calculation of those
pointers out into a separate function such that it can continue to be
shared.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: Niklas Cassel <niklas.cassel@axis.com>
Cc: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12337/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>