stm32: rework spi, based on PR #740 and #742.

split spi stuff in three part:
 - v1 : basic spi peripheral
 - v1_frf : v1 spi with frf mode additional bit in spi_cr2 / spi_sr
 - v2 : spi with variable datasize, fifo and other fancy stuff.

v1 maps to f1 chips
v1_frf to f2, f4 and l0,l1
v2 to f0, f3 and l4

This breaks spi_master_init API for v2 devices : function prototype from
common spi header used to be abused, with DFF bit reused for CRCL bit.
New v2 spi_master_init does not handle anymore CRCL bits, as it does not
usually mess with other crc configuration.

include/libopencm3/stm32/l0/spi.h

@@ -0,0 +1,37 @@
+/** @defgroup spi_defines SPI Defines
+
+@brief <b>Defined Constants and Types for the STM32L0xx SPI</b>
+
+@ingroup STM32L0xx_defines
+
+@version 1.0.0
+
+@date 20 January 2017
+
+LGPL License Terms @ref lgpl_license
+ */
+
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef LIBOPENCM3_SPI_H
+#define LIBOPENCM3_SPI_H
+
+#include <libopencm3/stm32/common/spi_common_v1_frf.h>
+
+#endif
+