flash: add virtual flash bank driver

This adds a virtual flash bank driver that allows virtual banks to
be defined that refer to an existing flash bank.

For example the real address for bank0 on the pic32 is 0x1fc00000
but the user program will either be in kseg0 (0xbfc00000) or
kseg1 (0x9fc00000).
This also means that gdb will be aware of all the read only flash
addresses.

Signed-off-by: Spencer Oliver <ntfreak@users.sourceforge.net>

src/flash/nor/drivers.c

@@ -39,6 +39,7 @@ extern struct flash_driver ocl_flash;
 extern struct flash_driver pic32mx_flash;
 extern struct flash_driver avr_flash;
 extern struct flash_driver faux_flash;
+extern struct flash_driver virtual_flash;
 
 /**
  * The list of built-in flash drivers.
@@ -63,6 +64,7 @@ static struct flash_driver *flash_drivers[] = {
 	&pic32mx_flash,
 	&avr_flash,
 	&faux_flash,
+	&virtual_flash,
 	NULL,
 };