Adjust "hack/make/.detect-daemon-osarch" to be the source of truth for "platform detection"

Instead of being split between three files, let's let `hack/make/.detect-daemon-osarch` be our single source of truth for multiarch detection/vars.  Not only does it make it slightly easier to make sure we change everything properly when these bits have to change, but it also makes it so that all bits of `hack/make.sh` (especially `hack/make/.ensure-frozen-images`) work properly outside the context of the `Makefile` on all platforms.

Signed-off-by: Andrew "Tianon" Page <admwiggin@gmail.com>

Makefile

@@ -1,30 +1,8 @@
 .PHONY: all binary build cross default docs docs-build docs-shell shell test test-docker-py test-integration-cli test-unit validate
 
 # get OS/Arch of docker engine
-DOCKER_OSARCH := $(shell bash -c 'source hack/make/.detect-daemon-osarch && echo $${DOCKER_ENGINE_OSARCH:+$$DOCKER_CLIENT_OSARCH}')
-# default for linux/amd64 and others
-DOCKERFILE := Dockerfile
-# switch to different Dockerfile for linux/arm
-ifeq ($(DOCKER_OSARCH), linux/arm)
-	DOCKERFILE := Dockerfile.armhf
-else
-ifeq ($(DOCKER_OSARCH), linux/arm64)
-	DOCKERFILE := Dockerfile.aarch64
-else
-ifeq ($(DOCKER_OSARCH), linux/ppc64le)
-	DOCKERFILE := Dockerfile.ppc64le
-else
-ifeq ($(DOCKER_OSARCH), linux/s390x)
-	DOCKERFILE := Dockerfile.s390x
-else
-ifeq ($(DOCKER_OSARCH), windows/amd64)
-	DOCKERFILE := Dockerfile.windows
-endif
-endif
-endif
-endif
-endif
-export DOCKERFILE
+DOCKER_OSARCH := $(shell bash -c 'source hack/make/.detect-daemon-osarch && echo $${DOCKER_ENGINE_OSARCH:-$$DOCKER_CLIENT_OSARCH}')
+DOCKERFILE := $(shell bash -c 'source hack/make/.detect-daemon-osarch && echo $${DOCKERFILE}')
 
 # env vars passed through directly to Docker's build scripts
 # to allow things like `make DOCKER_CLIENTONLY=1 binary` easily
@@ -37,7 +15,6 @@ DOCKER_ENVS := \
 	-e DOCKER_CLIENTONLY \
 	-e DOCKER_DEBUG \
 	-e DOCKER_EXPERIMENTAL \
-	-e DOCKERFILE \
 	-e DOCKER_GRAPHDRIVER \
 	-e DOCKER_INCREMENTAL_BINARY \
 	-e DOCKER_REMAP_ROOT \