package/ti-sgx-libgbm: new package

package/ti-sgx-libgbm: new package

A custom ti version of libgbm for SGX graphics accelerator, required by
the binary libraries of the ti-sgx-um package.

Signed-off-by: Lothar Felten <lothar.felten@gmail.com>
Signed-off-by: Carlos Santos <unixmania@gmail.com>
[Thomas:
 - fix LICENSE variable, as noticed by Yegor
 - fix alphabetic ordering in package/Config.in
 - add missing select BR2_PACKAGE_LIBDRM in Config.in, and the
   corresponding dependencies
 - add missing depends on BR2_PACKAGE_HAS_UDEV in Config.in
 - use gbm.h as license file, instead of extracting the first 26 lines
   of the header file]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>