wil6210: make debugfs compilation optional

Since debugfs is a kernel configuration option, enable the driver to
compile without debugfs.

Change-Id: Id1b162172e2662a59af5b031a71ccd22250e4b6d
Signed-off-by: Gidon Studinski <qca_gidons@qca.qualcomm.com>
Signed-off-by: Hamad Kadmany <qca_hkadmany@qca.qualcomm.com>
Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
Git-commit: 5f591dac9f20f76439df2e18570765d384a94070
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git


Signed-off-by: Maya Erez <merez@codeaurora.org>