Update u-boot-brain / append the updated way to run udefconfig

Makefile

@@ -27,6 +27,10 @@ watch:
 udefconfig:
 	make -C ./u-boot-brain pwsh1_defconfig
 
+.PHONY:
+udefconfig-%:
+	make -C ./u-boot-brain pw$*_defconfig
+
 .PHONY:
 usavedefconfig:
 	make -C ./u-boot-brain savedefconfig

README.md

@@ -44,7 +44,10 @@ Getting Started
 Build and inject U-Boot
 -----------------------
 
-1. Run `make udefconfig` to generate `.config`.
+1. Run `make udefconfig-sh*` to generate `.config`.
+
+    - For Sx1: `make udefconfig-sh1`
+    - For Sx6: `make udefconfig-sh6`
 
 2. Run `make ubuild` to build whole repository and generate `u-boot.sb`.