mac80211: aead api to reduce redundancy

Currently, the aes_ccm.c and aes_gcm.c are almost line by line copy of
each other. This patch reduce code redundancy by moving the code in these
two files to crypto/aead_api.c to make it a higher level aead api. The
file aes_ccm.c and aes_gcm.c are removed and all the functions there are
now implemented in their headers using the newly added aead api.

Signed-off-by: Xiang Gao <qasdfgtyuiop@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>