vc4: Enable NEON asm on meson cross-builds.

The core Mesa with_asm_arch and USE_ARM_ASM flags are disabled for meson
cross-builds because of the need to run host binaries on the build system.
vc4 doesn't need to do that, so skip with_asm_arch to enable NEON on my
cross-builds.

Fixes: ebcb4c21 ("meson: Enable VC4's NEON assembly support.")
(cherry picked from commit 932ed9c0)