target: declare local symbols as static

target: declare local symbols as static

Functions and variables that are not used outside the file should
be declared as static.

Change-Id: I9f97571a528f0cb3c3c26f873577ab16fdec3cdc
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5895
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>