This requires sorting the spilled variables based on alignment and
introducing additional padding around the spill location areas.

These changes allow vector instructions to accept memory operands.

Old stack frame layout:  New stack frame layout:
+---------------------+  +---------------------+
| return address      |  | return address      |
+---------------------+  +---------------------+
| preserved registers |  | preserved registers |
+---------------------+  +---------------------+
| global spill area   |  | padding             |
+---------------------+  +---------------------+
| local spill area    |  | global spill area   |
+---------------------+  +---------------------+
| padding             |  | padding             |
+---------------------+  +---------------------+
| local variables     |  | local spill area    |
+---------------------+  +---------------------+
                         | padding             |
                         +---------------------+
                         | local variables     |
                         +---------------------+

BUG=none
R=jvoung@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/465413003