[pprzlink] add read macros for all telemetry class

- support aligned or non aligned data depending of the arch
- Define PPRZLINK_UNALIGNED_ACCESS to TRUE if the target CPU/MMU allows unaligned access.
  This is true for x86/64 and most recent ARM platforms (ARMv7, Cortex-A, Cortex-M3/4).
  Examples for targets WITHOUT unaligned access support: LPC21xx, Cortex-M0
- will help air-to-air communications (#1509)

conf/Makefile.nps

@@ -52,6 +52,9 @@ CXXFLAGS += $(shell pkg-config --cflags-only-I ivy-glib)
 
 LDFLAGS	+= $($(TARGET).LDFLAGS) -pthread
 
+# x86/64 and armv7 allow unaligned access
+CFLAGS += -DPPRZLINK_UNALIGNED_ACCESS=1
+
 #
 # General rules
 #