coresight: move of_coresight.c to drivers/of

Move of_coresight.c from drivers/coresight to drivers/of where
all the of drivers files belong. of_coresight.c compilation will
now depend on CONFIG_CORESIGHT. Also make other appropriate
changes to Kconfig and Makefiles to support this.

This will allow other drivers using of_coresight.c apis to
compile and link successfully even when CONFIG_CORESIGHT is
disabled.

Change-Id: I05a32cb3f15767adf10de0a6b4b133e85a70e710
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>