package/libeastl: new package

package/libeastl: new package

This patch adds the Entertainment Arts Standard Template Library.

The initial version uses the latest hash so that the aarch64 support
is included vs Buildroot having to apply the aarch64 support patch.

Signed-off-by: Maury Anderson <maury.anderson@rockwellcollins.com>
Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
[Thomas:
 - add missing BR2_INSTALL_LIBSTDCPP dependency
 - use the github helper instead of the git site method, and adjust
   hash consequently
 - drop INSTALL_TARGET_CMDS, the default cmake-package implementation
   works fine]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>