genksyms: Do not expand internal types

Consider structures, unions and enums defined in the source file as
internal and do not expand them. This way, changes to e.g. struct
serial_private in drivers/tty/serial/8250_pci.c will not affect the
checksum of the pciserial_* exports.

diff --cc scripts/genksyms/genksyms.c
Simple merge

diff --cc scripts/genksyms/genksyms.h
Simple merge

diff --cc scripts/genksyms/lex.l
Simple merge

diff --cc scripts/genksyms/parse.y
Simple merge