meson_options.txt: Support for reading options from meson.options

Support has been added for reading options from meson.options instead
of meson_options.txt[1]. These are equivalent, but not using the .txt
extension for a build file has a few advantages, chief among them
many tools and text editors expect a file with the .txt extension to
be plain text files, not build scripts.

[1] https://mesonbuild.com/Release-notes-for-1-1-0.html#support-for-reading-options-from-mesonoptions

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: I93dec606f71f1bccc1e78cc892aeadb96394f125
diff --git a/meson_options.txt b/meson.options
similarity index 100%
rename from meson_options.txt
rename to meson.options