UBUNTU: [Packaging] introduce do_lib_rust and enable it only on generic amd64

Introduce the new variable do_lib_rust to enable or disable the
packaging of linux-lib-rust and enable it only on the generic amd64
kernel.

This allows to avoid building any kind of Rust artifact in other
kernels, except for the generic one and only on amd64.

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

debian.master/rules.d/amd64.mk

@@ -21,3 +21,4 @@ do_extras_package = true
 do_tools_common = true
 do_tools_acpidbg = true
 do_odm_drivers  = true
+do_lib_rust     = true

debian/rules.d/1-maintainer.mk

@@ -82,6 +82,7 @@ printenv:
 	@echo "do_common_headers_indep   = $(do_common_headers_indep)"
 	@echo "do_full_source            = $(do_full_source)"
 	@echo "do_odm_drivers            = $(do_odm_drivers)"
+	@echo "do_lib_rust               = $(do_lib_rust)"
 	@echo "do_tools                  = $(do_tools)"
 	@echo "do_tools_common           = $(do_tools_common)"
 	@echo "do_any_tools              = $(do_any_tools)"

debian/rules.d/2-binary-arch.mk

@@ -132,7 +132,7 @@ $(stampdir)/stamp-install-%: $(stampdir)/stamp-build-% $(stampdir)/stamp-install
 	dh_prep -p$(bin_pkg_name)-$*
 	dh_prep -p$(mods_pkg_name)-$*
 	dh_prep -p$(hdrs_pkg_name)-$*
-ifeq ($(build_arch),x86)
+ifeq ($(do_lib_rust),true)
 	dh_prep -p$(rust_pkg_name)-$*
 endif
 	$(foreach _m,$(all_standalone_dkms_modules), \
@@ -651,7 +651,7 @@ endif
 
 	$(call dh_all,$(pkgbldinfo))
 	$(call dh_all,$(pkghdr))
-ifeq ($(build_arch),x86)
+ifeq ($(do_lib_rust),true)
 	$(call dh_all,$(pkgrust))
 endif