MIPS64: Fix push the formal parameter count argument to the generator function.

TEST: mjsunit/harmony/generators-iteration
MIPS64: Add TODO(s).

Need find a good way to fix this.
MIPS64: Comment SharedFunctionInfo::kFormalParameterCountOffset usage.

The FormalParameterCount (arg count) is a Smi on 32-bits, and is a
int32_t on 64-bit platforms. This will require special handling
if/when we do a unified port. Added a TODO to all usages.

No code change.
MIPS64: port: Fix dictionary element load to pass correct elements kind.

Back-merge r19387, and adapt for mips64.

Using FAST_SMI_ELEMENTS triggers optimization on 64-bit architectures that load
only the higher 32 bits of the element. If the element is a pointer to undefined
that has 0 in the higher half than it is erroneously treated as SMI 0.

BUG=v8:3158
LOG=N
TEST=mjsunit/sparse-array-reverse,mjsunit/regress/regress-3158.js
R=danno@chromium.org, ishell@chromium.org

Review URL: https://codereview.chromium.org/166653005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19387 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

Conflicts:
	test/mjsunit/mjsunit.status