stm32: quadspi overhaul documentation

Provide all doxygen framework boilerplate.
Provide a very initial stub .c file to ensure that heirarchical headers
are pulled in properly.

lib/stm32/common/quadspi_common_v1.c

@@ -0,0 +1,12 @@
+
+#include <libopencm3/stm32/quadspi.h>
+
+void quadspi_enable(void)
+{
+	QUADSPI_CR |= QUADSPI_CR_EN;
+}
+
+void quadspi_disable(void)
+{
+	QUADSPI_CR &= ~QUADSPI_CR_EN;
+}

lib/stm32/f4/Makefile

@@ -64,6 +64,7 @@ OBJS += rtc_common_l1f024.o rtc.o
 OBJS += spi_common_all.o spi_common_v1.o spi_common_v1_frf.o
 OBJS += timer_common_all.o timer_common_f0234.o timer_common_f24.o
 OBJS += usart_common_all.o usart_common_f124.o
+OBJS += quadspi_common_v1.o
 
 OBJS += usb.o usb_standard.o usb_control.o usb_msc.o
 OBJS += usb_hid.o

lib/stm32/h7/Makefile

@@ -48,6 +48,7 @@ OBJS += rng_common_v1.o
 OBJS += spi_common_all.o spi_common_v2.o
 OBJS += timer_common_all.o
 OBJS += usart_common_v2.o usart_common_fifos.o
+OBJS += quadspi_common_v1.o
 
 VPATH += ../../usb:../:../../cm3:../common