NFC: st21nfca: Fix potential depmod dependency cycle

In the previous makefile 2 modules were generated for CONFIG_NFC_ST21NFCA
(st21nfca.ko and st21nfca_dep.ko). Merge both of them into st21nfca_hci.ko
and fix a potential depmod dependency cycle, similar to the one we saw
on st21nfcb:

depmod: WARNING: found 6 modules in dependency cycles!
depmod: WARNING:
/lib/modules/3.17.0-rc3-00002-g7505cea/kernel/drivers/nfc/st21nfcb/st21nfcb.ko
in dependency cycle!
depmod: WARNING:
/lib/modules/3.17.0-rc3-00002-g7505cea/kernel/drivers/nfc/st21nfcb/ndlc.ko
in dependency cycle!
depmod: WARNING:
/lib/modules/3.17.0-rc3-00002-g7505cea/kernel/net/rfkill/rfkill.ko in
dependency cycle!
depmod: WARNING:
/lib/modules/3.17.0-rc3-00002-g7505cea/kernel/net/nfc/nfc.ko in
dependency cycle!
depmod: WARNING:
/lib/modules/3.17.0-rc3-00002-g7505cea/kernel/net/nfc/nci/nci.ko in
dependency cycle!
depmod: WARNING:
/lib/modules/3.17.0-rc3-00002-g7505cea/kernel/lib/crc-ccitt.ko in
dependency cycle!
./scripts/depmod.sh: line 57: 23387 Segmentation fault      (core
dumped) "$DEPMOD" "$@" "$KERNELRELEASE" $SYMBOL_PREFIX
make: *** [_modinst_post] Error 139

Reported-by: Daniel Wagner <wagi@monom.org>
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>