linux-firmware: support paths with subdirs in LINUX_FIRMWARE_DIRS

linux-firmware: support paths with subdirs in LINUX_FIRMWARE_DIRS

Following commit cdb7876f63a253254b86637aaac8b255a426b60a
("linux-firmware: add Qualcomm video accelerator and GPU firmware
options"), LINUX_FIRMWARE_DIRS can now contain entries with subdirs,
such as "qcom/venus-1.8". Such entries are currently not supported by
the logic in LINUX_FIRMWARE_INSTALL_DIRS.

Indeed the current logic consists in:

 - Removing the destination directory
 - Copying to the destination directory

Unfortunately, the last step fails if a component of the path leading
to the destination directory does not exist. To overcome this, we
simply add the appropriate mkdir before the copy.

Fixes:

  http://autobuild.buildroot.net/results/54cbca90742faf486e59d95b95a0b0494e47b385/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>