vc4: Use a wrapper file to set VC4_BUILD_NEON instead of CFLAGS.

Android.mk was setting the flag across the entire driver, so we didn't
have non-NEON versions getting built.  This was going to be a problem with
the next commit, when I start auto-detecting NEON support and use the
non-NEON version when appropriate.

Reviewed-by: Rob Herring <robh@kernel.org>

src/gallium/drivers/vc4/Makefile.am

@@ -41,10 +41,4 @@ libvc4_la_SOURCES = $(C_SOURCES)
 libvc4_la_LIBADD = $(SIM_LIB) $(VC4_LIBS)
 libvc4_la_LDFLAGS = $(SIM_LDFLAGS)
 
-noinst_LTLIBRARIES += libvc4_neon.la
-libvc4_la_LIBADD += libvc4_neon.la
-
-libvc4_neon_la_SOURCES = vc4_tiling_lt.c
-libvc4_neon_la_CFLAGS = $(AM_CFLAGS) -DVC4_BUILD_NEON
-
 EXTRA_DIST = kernel/README