linux: install firmware to staging.

Install firmware to staging when the hidden option
BR2_LINUX_KERNEL_INSTALL_FIRMWARE is selected.  This allows parts of the
firmware provided by the linux kernel to be installed in the target.

Signed-off-by: Spenser Gilliland <spenser@gillilanding.com>
beagle-capes: new package

installs cape dtbos from the kernel firmware into the target system.

Signed-off-by: Spenser Gilliland <spenser@gillilanding.com>