genksyms: pass hash and lookup functions name and target language though the input file

Renaming hash and lookup functions on the command line would reduces its
genericity. Use the .gperf file to pass this information. Do the same for the
target language.
Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>

scripts/genksyms/keywords.gperf

+%language=ANSI-C
+%define hash-function-name is_reserved_hash
+%define lookup-function-name is_reserved_word
 %{
 struct resword;
 static const struct resword *is_reserved_word(register const char *str, register unsigned int len);