ltq-deu: remove redundant code for setting the key in aes

ltq-deu: remove redundant code for setting the key in aes

After adding xts and cbcmac the aes algorithm source had three sections
for setting the aes key to the hardware which are identical.
Method aes_set_key_hw was created which is now called from within the
spinlock secured control sections in methods ifx_deu_aes, ifx_deu_aes_xts
and aes_cbcmac_final_impl and reduces the size of ifxmips_aes.c.

Signed-off-by: Daniel Kestrel <kestrel1974@t-online.de>