stm32f1: Increase block size of GD32F3/F2 to 2 KiB in first bank

* Both GD32F205 (HD) / F207 (CL) and GD32F30x_HD/_XD/_CL have their flash in erase blocks of 2 KiB
* Save some time by not submitting 1 KiB-wise erase commands on these targets

src/target/stm32f1.c

@@ -149,16 +149,19 @@ bool gd32f1_probe(target_s *target)
 	case 0x414U: /* Gigadevice gd32f303 */
 	case 0x430U: /* XL-density */
 		target->driver = "GD32F3";
+		block_size = 0x800;
 		break;
 	case 0x418U:
 		target->driver = "GD32F2";
+		block_size = 0x800;
 		break;
 	case 0x410U: /* Gigadevice gd32f103, gd32e230 */
 		if ((target->cpuid & CORTEX_CPUID_PARTNO_MASK) == CORTEX_M23)
 			target->driver = "GD32E230";
-		else if ((target->cpuid & CORTEX_CPUID_PARTNO_MASK) == CORTEX_M4)
+		else if ((target->cpuid & CORTEX_CPUID_PARTNO_MASK) == CORTEX_M4) {
 			target->driver = "GD32F3";
-		else
+			block_size = 0x800;
+		} else
 			target->driver = "GD32F1";
 		break;
 	case 0x444U: /* Gigadevice gd32e50x */