firmware: add support for PCMCIA Aircard's

Add .cis firmware for Sierra Wireless Aircard GPRS/3G PCMCIA modems:

 - Aircard 555
 - Aircards 7xx
 - Aircards 8x0

There is a package named sierra-pcmcia in obsoleted repository for
packages at git.openwrt.org but there's no reason to reintroduce it in
current packages repo because these files are part of upstream
linux-firmware.

Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>

package/firmware/linux-firmware/cis.mk

@@ -0,0 +1,10 @@
+Package/aircard-pcmcia-firmware = $(call Package/firmware-default,Sierra Wireless Aircard 555/7xx/8x0 firmware)
+define Package/aircard-pcmcia-firmware/install
+	$(INSTALL_DIR) $(1)/lib/firmware/cis
+	$(INSTALL_DATA) \
+		$(PKG_BUILD_DIR)/cis/SW_555_SER.cis \
+		$(PKG_BUILD_DIR)/cis/SW_7xx_SER.cis \
+		$(PKG_BUILD_DIR)/cis/SW_8xx_SER.cis \
+		$(1)/lib/firmware/cis
+endef
+$(eval $(call BuildPackage,aircard-pcmcia-firmware))