Move flashcode to shared gd32_fmc layer

Refactors flash read/erase/write logic out of lib-flashcode into a new shared `gd32::fmc` API in `lib-gd32` (`gd32_fmc.h` plus F/F4 implementations), and updates `FlashCode` to delegate to that API. Removes old family-specific flashcode/FMC files, adds FMC debug macros, and adjusts GD32 makefiles/rules to pull sources/includes from the new structure. Also adds GD32F10X softuart0 timer/IRQ mapping support.

Author: vanvught

lib-flashcode/Makefile.GD32

@@ -1,18 +1,8 @@
 DEFINES =NDEBUG
 
-ifneq ($(MAKE_FLAGS),)
-	ifeq ($(findstring gd32f4xx,$(FAMILY)), gd32f4xx)
-		EXTRA_SRCDIR=src/gd32/f4xx
-	else
-		ifeq ($(findstring gd32h7xx,$(FAMILY)), gd32h7xx)
-			EXTRA_SRCDIR=src/gd32/h7xx
-		else
-			EXTRA_SRCDIR=src/gd32/fmc
-		endif
-	endif
-else
-	EXTRA_SRCDIR=src/gd32/fmc
-endif
+EXTRA_INCLUDES=../lib-gd32/include ../lib-gd32/src
+
+EXTRA_SRCDIR=src/spi/gd32
 
 include Rules.mk
 include ../firmware-template-gd32/lib/Rules.mk