i965: add helpers for creating component layout swizzle
i965: add helpers for creating component layout swizzle

This will be used to swizzle components to the beginning or end
of the vector based on the component layout qualifier and whether
we are doing a load or store.

Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Reviewed-by: Edward O'Callaghan <b035da0d7e151e09fe2005f3a7bc526beb9b3245@folklore1984.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler