Add a README file for the source code repository of KGSL driver outlining
driver's purpose, dev branch details, build instructions, procedures for
reporting issues and licensing details. Additionally, include the full
text of the GPL v2.0 license.

Change-Id: I7736bf36db6f9a9af5f8b2a1341b43bc4d657a22
Signed-off-by: Kaushal Sanadhya <quic_ksanadhy@quicinc.com>