Add IRAM attribute for IRAM loaded symbols, add to common FreeRTOS functions

Closes #7.

It'd be nice to change the linker script so .text is always linked to
IROM instead of needing to objcopy each compiled file. The sticking
point for this is libgcc & libhal, which have symbols in .text that need
to be loaded to IRAM.

core/include/common_macros.h

@@ -30,4 +30,6 @@
 
 #define INLINED inline static __attribute__((always_inline)) __attribute__((unused))
 
+#define IRAM __attribute__((section(".iram1.text")))
+
 #endif