coresight: check if gpio count is positive before using

If gpio entries are not present in dt file, the resource query
function returns negative value for gpio count. Currently data
type for gpio count is unsigned int which wraps around and gives
positive result for negative value that causes failure while
probing the driver. Modify gpio count data type to integer and
check if it is positive before using it.

Change-Id: I1596f3d1090f5caa70735c66e10f82914ac7ab26
Signed-off-by: Sarang Joshi <spjoshi@codeaurora.org>