brcmfmac: add CLM download support

The firmware for brcmfmac devices includes information regarding
regulatory constraints. For certain devices this information is kept
separately in a binary form that needs to be downloaded to the device.
This patch adds support to download this so-called CLM blob file. It
uses the same naming scheme as the other firmware files with extension
of .clm_blob.

The CLM blob file is optional. If the file does not exist, the download
process will be bypassed. It will not affect the driver loading.

Reviewed-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Chung-Hsien Hsu <stanley.hsu@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>