build: add cscope support
build: add cscope support

This will create a new target in the Makefile, allowing devvers to enjoy cscope
utility just by typing 'make cscope'.

'make clean' will also clean up the intermediate cscope files.

Signed-off-by: Liu Yuan <ebb1e794c7d5400b1c3370749547ed12137bd932@cmss.chinamobile.com>

open-iscsi/tcmu-runner,open-iscsi/tcmu-runner,JefferyHu/tcmu-runner,agrover/tcmu-runner,lxbsz/tcmu-runner,liuy/tcmu-runner,superlibj/tcmu-runner