Revert "ARM: errata: work around Cortex-A15 erratum 830321 using dummy strex"

This reverts commit 83a231d4c9416161d0a62f8a63590dbf5650a419.
Revert "ARM: abort: don't clear the exclusive monitors"

This reverts commit 750574fa5983aea798f6af989254fc6e4b6f5468.