fpga/fw: Resize ROM and FW_RAM, add RESETINFO partition

In order to be able to leave data for firmware signalling the
intention with a reset or to leave data for the next app in a chain of
apps, we introduce a part of FW_RAM that can be used to store this
data. In order to do this, we:

- Change size of ROM from 6 KB to 8 KB.
- Change size of FW_RAM, from 2 KB to 4 KB.
- Add RESETINFO memory partition inside FW_RAM.
- Add generation of map file.
- Change CFLAGS from using -O2 to using -Os.
- Update address ranges for valid access to ROM and FW_RAM.
- Move stack to be located before data+bss and the RESETINFO data
  above them. This also means we introduce hardware stack overflow
  protection through the Security Monitor.
- Revise firmware README to the new use of FW_RAM.

hw/application_fpga/fw/tk1/start.S

@@ -39,17 +39,24 @@ _start:
 	li x31,0
 
 	/* Clear FW_RAM */
-	li a0, 0xd0000000 // TK1_MMIO_FW_RAM_BASE
-	li a1, 0xd0000800 // TK1_MMIO_FW_RAM_BASE + TK1_MMIO_FW_RAM_SIZE
+	la a0, _sfwram
+	la a1, _efwram
 clear:
 	sw zero, 0(a0)
 	addi a0, a0, 4
 	blt a0, a1, clear
 
-        /*
-         * Init stack at top of fw_ram.
-         */
-        li sp, 0xd0000800 // 2 kiB (TK1_MMIO_FW_RAM_SIZE)
+	/* Zero-init bss section */
+	la a0, _sbss
+	la a1, _ebss
+
+loop_init_bss:
+	sw zero, 0(a0)
+	addi a0, a0, 4
+	blt a0, a1, loop_init_bss
+
+	/* Init stack */
+	la sp, _estack
 
 	call main