Add support for FrSky OSD

- Add displayWriteFontCharacter() for font writing, removing all max7456
specific code.
- Add displayIsReady() for asynchronous display initialization
- Add displayBeginTransaction()/displayCommitTransaction() for display
transactions, which allow performing complex drawing operations without
flickering
- Add displayGetCanvas(), which retrieves the canvas associated with a
display (if it has it)
- Add canvas implementation for pixel based access for a display
- Add FrSkyOSD driver and displayPort driver
- Enable FrSkyOSD driver for targets with flash > 256
- Rename max7456_symbols.h to osd_symbols.h

src/test/Makefile

@@ -439,9 +439,11 @@ COMMON_FLAGS = \
 ifeq ($(shell $(CC) -v 2>&1 | grep -q "clang version" && echo "clang"),clang)
 COMMON_FLAGS += -fblocks
 ifndef CYGWIN
+ifndef MACOSX
 LDFLAGS	     += -lBlocksRuntime
 endif
 endif
+endif
 
 USE_PTHREAD = YES
 USE_COVERAGE = YES

src/test/unit/link_quality_unittest.cc

@@ -33,7 +33,7 @@ extern "C" {
     #include "common/printf.h"
     #include "common/streambuf.h"
 
-    #include "drivers/max7456_symbols.h"
+    #include "drivers/osd_symbols.h"
     #include "drivers/persistent.h"
     #include "drivers/serial.h"
     #include "drivers/system.h"

src/test/unit/osd_unittest.cc

@@ -36,7 +36,7 @@ extern "C" {
 
     #include "common/time.h"
 
-    #include "drivers/max7456_symbols.h"
+    #include "drivers/osd_symbols.h"
     #include "drivers/persistent.h"
     #include "drivers/serial.h"