fuchsia: Remove all references to FUCHSIA(X) for non-Fuchsia builds

This change adds #ifdefs to make sure that all references
to FUCHSIA(X) identifiers are only used on Fuchsia builds
where VK_USE_PLATFORM_FUCHSIA is defined.

Bug: 187216205
Change-Id: I950327500edf6816da6d2d918ad39f4044d9572a
3 files changed