fix realtek_rtl8195am IPv6 build fails

remove the "dhcps.h" and "dhcps.c" files
edit "wifi_conf.c" and "rtw_emac.cpp" to fix compile error
coding style fix

Author: M-ichae-l

targets/TARGET_Realtek/TARGET_AMEBA/rtw_emac.cpp

@@ -56,7 +56,7 @@ void RTW_EMAC::get_ifname(char *name, uint8_t size) const
 
 uint8_t RTW_EMAC::get_hwaddr_size() const
 {
-    return ETHARP_HWADDR_LEN;
+    return ETH_HWADDR_LEN;
 }
 
 bool RTW_EMAC::get_hwaddr(uint8_t *addr) const