tools/alpine: multi-arch support for the base alpine image

Alpine is the base docker image for the LinuxKit, but currently
it only supports amd64 architecture. This patch is try to unify
the alpine tool docker image build process order to suport other
architectures, such as AArch64, by using '--build-arg' to override
the alpine base image specified by 'FROM' in the Dockerfile.

Also this patch splits the standalone packages into 2 parts:
one is common for all archs, another is arch-specific.

Signed-off-by: Dennis Chen <dennis.chen@arm.com>

tools/alpine/packages

@@ -61,7 +61,6 @@ openntpd
 openrc
 openssh-server
 openssl-dev
-open-vm-tools
 patch
 python3
 qemu-aarch64
@@ -77,7 +76,6 @@ slang-dev
 squashfs-tools
 strace
 swig
-syslinux
 tar
 tcpdump
 tini