MIPS: Always read full 64 bit CM error GCRs for CM3

CM3 has 64 bit GCR_ERROR_* registers, but the code in
mips_cm_error_report was previously only reading 32 bits of it in MIPS32
kernels. Fix by splitting the reads for CM2 & CM3, and making use of the
read64_ variants of the accessor function for CM3.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/11189/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>