MIPS64: Representation fix for DoLoadKeyedFixedArray()

When the representation is Integer32, we need to load this Smi
as an integer, effectively untagging it during the load.

TEST=mjsunit/keyed-ic, mjsunit/keyed-call-ic, mjsunit/arguments
(and many others)
MIPS64: Fix sim stack-printing and tweak reg dumps.

The stack printing used 32-bit values, and needed to be fixed.
The register dump change was just print formatting, still not
sure it is optimal.
Merge remote-tracking branch 'origin/pl-mips64' into yy-dev-mips64
MIPS64: Remove all break_ and fix InstanceofStub/DoStoreNamedField/DoStoreKeyedFixedArray.