devtools: add tags and cscope index generation

devtools: add tags and cscope index generation

This script generates cscope, gtags, and tags index files based on
EAL environment(architecture and OS(linux/bsd)).

Selection of the architecture and OS environment is based on dpdk
configuration target(T=).If EAL environment(T=) is not specified,
the script generates tag files based on available source code.

Usage: make tags|cscope|gtags|etags [T=config]

example usage:
make cscope
make tags T=x86_64-native-linuxapp-gcc
make gtags T=arm64-armv8a-linuxapp-gcc

Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Reviewed-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
Reviewed-by: Thomas Monjalon <thomas@monjalon.net>