[stm32f7] Add initial support of the family, GPIO support.

Most changes are noise from doxygen.
Readme udpated to explain newer FP_FLAGS for m7
stm32f7 library is skipped if the toolchain doesn't support it yet.

lib/stm32/f7/gpio.c

@@ -0,0 +1,31 @@
+/** @defgroup gpio_file GPIO
+
+@ingroup STM32F7xx
+
+@brief <b>libopencm3 STM32F7xx General Purpose I/O</b>
+
+@version 1.0.0
+
+@date 18 August 2012
+
+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/>.
+ */
+
+#include <libopencm3/stm32/gpio.h>