kconfig: add CONFIG_CC_COVERAGE

Make it possible to use gcc code coverage analysis.

v1 -> v2:
 - Kconfig: remove not needed 'default n'
 - Makefile: use consistent spacing

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
3 files changed