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/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