classes/insane.bbclass: Add a small elf reader and check ABI,ARCH and Endian

classes/insane.bbclass: Add a small elf reader and check ABI,ARCH and Endian
Add a small ELF parser and read OSABI, ABIVERSION, ENDIAN and MACHINE. This
code compares TARGET_OS and TARGET_ARCH to a list of known versions. Currently
we have values for linux and linux-uclibc for arm, armeb and powerpc. mips,
i386, amd64, ia64 are missing. ABI wise ARM EABI is missing as well, but koen
is likely to enter the values into the documented dict