uavobjmgr: 4-byte align the load/save trampoline buffers

Any buffer used for DMA must be 4-byte aligned on F4 CPUs.
uavobjmgr: fix typo in uncompiled code path
uavobjmgr: correct FASTHEAP macro to enable trampoline buffers
Revert "F4 targets: disable PIOS_INCLUDE_FASTHEAP"

This reverts commit 0210ece5a3e02581cc95e9fc14b722aab6e16cd8.
Merge pull request #857 from solidgoldbomb/f4-fastram-fix

F4 fastram fix