Fix serial speed DD configuration & migrate keyboards (#25546)

* Fix serial speed DD configuration

- Fixes incorrect SOFT_SERIAL_SPEED mapping
- Renames key split.soft_serial_speed -> split.serial.speed
- Migrates keyoards that configure this, and remove configuration from keyboards that do not differ from the default behaviour
- Add deprecation notice and migration support

3 files changed, 2 insertions, 4 deletions

diff --git a/keyboards/zvecr/split_blackpill/config.h b/keyboards/zvecr/split_blackpill/config.h
index efc3bbe66a..59582a9726 100644
--- a/keyboards/zvecr/split_blackpill/config.h
+++ b/keyboards/zvecr/split_blackpill/config.h
@@ -2,8 +2,6 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 #pragma once
 
-#define SELECT_SOFT_SERIAL_SPEED 0
-
 #define WS2812_PWM_DRIVER PWMD3
 #define WS2812_PWM_CHANNEL 1
 #define WS2812_PWM_DMA_STREAM STM32_DMA1_STREAM3
diff --git a/keyboards/zvecr/split_blackpill/keyboard.json b/keyboards/zvecr/split_blackpill/keyboard.json
index 407314b71a..2884b790d7 100644
--- a/keyboards/zvecr/split_blackpill/keyboard.json
+++ b/keyboards/zvecr/split_blackpill/keyboard.json
@@ -27,7 +27,8 @@
         },
         "serial": {
             "driver": "usart",
-            "pin": "B6"
+            "pin": "B6",
+            "speed": 0
         },
         "bootmagic": {
             "matrix": [4, 0]
diff --git a/keyboards/zvecr/zv48/config.h b/keyboards/zvecr/zv48/config.h
index 9e8c2656a9..ab9ca3355b 100644
--- a/keyboards/zvecr/zv48/config.h
+++ b/keyboards/zvecr/zv48/config.h
@@ -3,7 +3,6 @@
 
 #pragma once
 
-//#define SELECT_SOFT_SERIAL_SPEED 0
 #define SERIAL_USART_SPEED 921600
 
 #define WS2812_PWM_DRIVER PWMD3