add more openrc subpackages

See: https://gitlab.com/postmarketOS/pmaports/-/issues/3045

modem/samsungipcd/APKBUILD

 # Maintainer: sleirsgoevy <sleirsgoevy@gmail.com>
 pkgname=samsungipcd
 pkgver=0.2.3
-pkgrel=0
+pkgrel=1
 pkgdesc="AT modem emulation using libsamsung-ipc"
 url="https://gitlab.com/sleirsgoevy/samsungipcd"
 arch="all"
 license="GPL-2.0-or-later"
 depends="libsamsung-ipc ppp networkmanager-ppp"
 makedepends="libsamsung-ipc gcc make"
+subpackages="$pkgname-openrc"
 source="
 	samsungipcd-v$pkgver.tgz::$url/-/archive/v$pkgver/samsungipcd-v$pkgver.tar.gz
-	samsungipcd.post-install
 	samsungipcd.sh
 	90-ttywc.rules
 "
-install="$pkgname.post-install"
 builddir="$srcdir/samsungipcd-v$pkgver"
 
 options="!check"
@@ -29,9 +28,15 @@ package() {
 	install -Dm644 "$srcdir/90-ttywc.rules" "$pkgdir/lib/udev/rules.d/90-ttywc.rules"
 }
 
+openrc() {
+	install_if="$pkgname=$pkgver-r$pkgrel openrc"
+	install="$subpkgname.post-install"
+
+	mkdir -p "$subpkgdir"
+}
+
 sha512sums="
 edf6e9f887bddc93daadbf1da05ef1ab75db4f3350d1b0fbbf1e90a9dd32dd3d13642aab83b50b5a43bac66889c982f40952b9f7351354a13525dde7f33a7414  samsungipcd-v0.2.3.tgz
-c1935d7421eb6d529fb827c438902fdcd47ced974b237c0d63403b8b70d8f53966c29585f4ebc89c66f261dfa97e893f2816a43cf69ed69ca5bb1b1798c22a1d  samsungipcd.post-install
 7bdc6cbc4a9add0f4a5a5d4584fbf4fc64cf4a1f0d93a85e97229eba47bbe66a8e0bd8958b4606141a0189422e13af252d3c0301f61069dc75a64e0a3b59d959  samsungipcd.sh
 2c93b98260a8b89d25bfc6bf554dc66f198846f35ed839069212aea2204b9cc92710ea7aa5c77003bd6952085018af1083640052094a115ba67257f9745f80bf  90-ttywc.rules
 "