Added rcGetGLString token to renderControl to query
a GL string constant from the current context from the host.
Implement glGetString functinality in EGL so that the string
value can be cached in the context structure and also
implementation can be shared between GLESv1 and GLESv2.
Also, fixed clientAPI context initialization check in
eglMakeCurrent. The check was for the previously bounded
context instead for the newly bounded context.
Change-Id: I41c0b4ad462c9ad5bd5c66719b41509bb1b7a947
1ef706f96f