build: eliminate obsolete hwf4-nouart target
build: mark platforms based on hwf4 compatibility

- since hwf4 is going away, we won't waste time making new platforms
  compatible with it
build: px4-hmc5883l and px4-ms5611 tests marked to only work on fmu17
buid: add px4fmu24 (pixhawk main mcu) platform
platform hs files updated for px4fmu24 platform where possible
build: factor linker memory map out into chip-configurable include file
ivory-bsp-stm32f4: remove deprecated functionality
fixups for ivory runCompiler changes
ivory-bsp-stm32f4: start adding support for vector table & init code
start renaming ivory-bsp-stm32f4 to ivory-bsp-stm32
ivory-bsp-stm32: more renaming
ivory-bsp-tests et al: fixes for ivory-bsp-stm32 renaming
ivory-bsp-stm32: fixes for moving types out into ARMv7M NVIC
ivory-bsp-stm32: vector table and init code fixes
flight: fixup for ivory-bsp-stm32 rename
ivory-bsp-stm32: init code preprocessor fixups
build: support assembler files in OBJECTS, -DTOWER_OS=xxx in CFLAGS
build: image.mk allows optionally disabling global startup files
px4 i2c device tests - build files fixed up
bsp-led-test and bsp-uart-test: disable global startup files, freertos main, echronos