Revert "Revert "correct config HAVE_EFFICIENT_UNALIGNED_ACCESS for ARM""

This reverts commit e30ca81fcfca1bd295c17ac2a4b5cd9af466512f.
Squashed update of kernel from 3.4.68 to 3.4.69

* also fix compile error by reverting commit
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=5812381adfde20cb352d3047190ab45ea5bb59f2
EXFAT: init sector value, and build in -O2