busybox: Enable CONFIG_SETSID

'setsid' binary is required for better MESA integration.

For details, please see:
http://jira.alm.mentorg.com:8080/browse/SB-1204
http://jira.alm.mentorg.com:8080/browse/SA-1888
 
Signed-off-by: Muhammad Shakeel <muhammad_shakeel@mentor.com>