Move LOADER_{NO,}_GELI_SUPPORT to MK_LOADER_GELI

Transition to WITH/WITHOUT_LOADER_GELI to flag support or not of GELI
in the boot loaders. Add HAVE_GELI so components can flag they need
support (since it's too large to include everywhere). Add temporary
warnings for the old forms to ease transition.

Also, update test script to build without GELI on x86.

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