Fix support of different attrib_list in eglGetPlatformDisplay

Regression was introduced by ag/5161774, where different
EGLDisplay(s) with the same display type but different
attrib_list(s) would share the same egl_display_t object.
Only the first EGLDisplay associated with the egl_display_t
would be initialized.

Bug: 162381841
Test: Run android.graphics.cts.EGL15Test in CtsGraphicsTestCases
Change-Id: I4419e0f9f0d0f6491e7fae397b6c8926405ca836