nn: add USE flag for building the minimal driver

BUG=b:154068977
TEST=USE=minimal-driver FEATURES=test emerge-betty \
     chromeos-base/aosp-frameworks-ml-nn

Cq-Depend: chromium:2282930
Change-Id: Iffe36df585e6cb299e46c69b48c9658160aed336
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2283304
Commit-Queue: Jim Pollock <jmpollock@chromium.org>
Commit-Queue: Stuart Langley <slangley@chromium.org>
Tested-by: Jim Pollock <jmpollock@chromium.org>
Reviewed-by: Stuart Langley <slangley@chromium.org>
Auto-Submit: Jim Pollock <jmpollock@chromium.org>
diff --git a/chromeos-base/aosp-frameworks-ml-nn/aosp-frameworks-ml-nn-9999.ebuild b/chromeos-base/aosp-frameworks-ml-nn/aosp-frameworks-ml-nn-9999.ebuild
index 91d3545..d2d3b69 100644
--- a/chromeos-base/aosp-frameworks-ml-nn/aosp-frameworks-ml-nn-9999.ebuild
+++ b/chromeos-base/aosp-frameworks-ml-nn/aosp-frameworks-ml-nn-9999.ebuild
@@ -32,7 +32,7 @@
 
 LICENSE="BSD-Google Apache-2.0"
 KEYWORDS="~*"
-IUSE="cpu_flags_x86_avx2 vendor-nnhal"
+IUSE="cpu_flags_x86_avx2 vendor-nnhal minimal-driver"
 
 RDEPEND="
 	chromeos-base/nnapi:=
@@ -55,10 +55,13 @@
 
 src_configure() {
 	if use x86 || use amd64; then
-		append-cxxflags "-D_Float16=__fp16"
+		append-cppflags "-D_Float16=__fp16"
 		append-cxxflags "-Xclang -fnative-half-type"
 		append-cxxflags "-Xclang -fallow-half-arguments-and-returns"
 	fi
+	if use minimal-driver; then
+		append-cppflags "-DNNAPI_USE_MINIMAL_DRIVER"
+	fi
 	platform_src_configure
 }