Implement EGL_KHR_gl_texture_cubemap_image support.
Implement EGL_KHR_gl_texture_cubemap_image support.

BUG=14610416

Change-Id: I1e236333c8fb7a6870bdd1ef8abaea4c6e9e4d4e
Reviewed-on: https://swiftshader-review.googlesource.com/1052
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

bkaradzic/SwiftShader,google/swiftshader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader