boot, package: use SPDX short identifier for BSD-3c

We want to use SPDX identifier for license string as much as possible.
SPDX short identifier for BSD-3c is BSD-3-Clause.

This change is done using following command.
find . -name "*.mk" | xargs sed -ri '/LICENSE( )?[\+:]?=/s/BSD-3c/BSD-3-Clause/g'

Signed-off-by: Rahul Bedarkar <rahulbedarkar89@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
diff --git a/package/libglew/libglew.mk b/package/libglew/libglew.mk
index 7af3aff..277a171 100644
--- a/package/libglew/libglew.mk
+++ b/package/libglew/libglew.mk
@@ -7,7 +7,7 @@
 LIBGLEW_VERSION = 2.0.0
 LIBGLEW_SOURCE = glew-$(LIBGLEW_VERSION).tgz
 LIBGLEW_SITE = http://sourceforge.net/projects/glew/files/glew/$(LIBGLEW_VERSION)
-LIBGLEW_LICENSE = BSD-3c, MIT
+LIBGLEW_LICENSE = BSD-3-Clause, MIT
 LIBGLEW_LICENSE_FILES = LICENSE.txt
 LIBGLEW_INSTALL_STAGING = YES
 LIBGLEW_DEPENDENCIES = libgl xlib_libX11 xlib_libXext xlib_libXi xlib_libXmu