[coreboot] pygen: code generation from xml files. step 1: msrtool module - fixes

[Антон Кочков]

msrtool: add support for code generation from xml files
Search all *.msr.xml files in directory, creating *.c files from them,
produce *.patch for msrtool.c and msrtool.h
Signed-off-by: Anton Kochkov 
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Small fixes, included export_msr.c file, which produce *.msr.xml files
from existing code