[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/Makefile

@@ -0,0 +1,70 @@
+##
+## This file is part of the libopencm3 project.
+##
+## Copyright (C) 2009 Uwe Hermann <uwe@hermann-uwe.de>
+## Copyright (C) 2013 Alexandru Gagniuc <mr.nuke.me@gmail.com>
+##
+## 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/>.
+##
+
+LIBNAME		= libopencm3_stm32f7
+SRCLIBDIR	?= ../..
+
+PREFIX		?= arm-none-eabi
+
+CC		= $(PREFIX)-gcc
+AR		= $(PREFIX)-ar
+
+# By default, use double precision FPU
+FP_FLAGS	?= -mfloat-abi=hard -mfpu=fpv5-d16
+
+CFLAGS		= -Os -g \
+		  -Wall -Wextra -Wimplicit-function-declaration \
+		  -Wredundant-decls -Wmissing-prototypes -Wstrict-prototypes \
+		  -Wundef -Wshadow \
+		  -I../../../include -fno-common \
+		  -mcpu=cortex-m7 -mthumb $(FP_FLAGS) \
+		  -Wstrict-prototypes \
+		  -ffunction-sections -fdata-sections -MD -DSTM32F7
+
+ARFLAGS		= rcs
+
+OBJS		= gpio.o gpio_common_all.o gpio_common_f0234.o
+
+VPATH += ../../usb:../:../../cm3:../common
+VPATH += ../../ethernet
+
+###############################################################################
+# Checking CPU support in the toolchain
+###############################################################################
+# TODO: This check and silent skip of build should be removed, when it will be
+# sure that first compatible toolchain (g-a-e 4.8 2014q3) will be sufficiently
+# penetrated in majority of user stations.
+define MISSING_CPU
+Your toolchain doesn't support -mcpu=cortex-m7.
+Please use gcc-arm-embedded 4.8 2014q3 or newer. Skipping this sub-library.
+endef
+
+ifneq ($(shell $(CC) -fsyntax-only -mcpu=cortex-m7 -mthumb -xc /dev/null 2>&1; echo $$?),0)
+  $(warning $(MISSING_CPU))
+
+all clean:
+	@true
+
+$(SRCLIBDIR)/$(LIBNAME).a:
+	@true
+
+else
+  include ../../Makefile.include
+endif