drivers/at86rf231: refactoring of the at86rf231 radio driver

* deploy extended operation mode
* cleanup
* implement netdev 802154.h interface
netdev/802154: suppress cppcheck warnings in 802154.h

Suppress cppcheck warnings of class unusedStructMember because
this interface is not used yet. Remove these comments once it
is used.
lint: fix unassignedVariable warnings in stm32f1
lint: fix unusedVariable warnings

SQUASH ME: into unusedVariable (annotated)

SQUASH ME: into unusedVariable (II)

SQUASH ME: into unreadVariable (II)
lint: fix redundantAssignment warnings

SQUASH ME: redundantAssignment (remove FAT stuff)

SQUASH ME: into redundantAssignment unnecessary supp
lint: fix unreadVariable warnings
lint: fix variableScope warnings
lint: fix invalidPrintfArgType_sint  warning
lint: fix uselessAssignmentPtrArg
lint: fix warnings of possible nullPointer dereferences
lint: fix nullPointer errors
lint: fix syntaxError warning
cpu: stm32f1 spi: fix typos
lint: suppress warning about obsoleteFuntionsasctime
lint: suppress unusedStructMember in vendor files
lint: fix redundantCopy in udp code
lint: fix va_end_missing in cpu/native/syscalls.c
lint: fix uninitstring in sixlowdriver
Merge pull request #1820 from N8Fear/cppcheck-cleanup

lint: take care of various warnings/errors issued by cppcheck
Merge pull request #1846 from thomaseichinger/at86rf23x

drivers/at86rf231: refactoring of the at86rf231 radio driver