Add support for MKS Robin board (#12650)

Implement initial support for MKS Robin (STM32F103ZET6) board.
Custom build script is used to generate encrypted firmware compatible with original MSK Robin bootloader (i.e. safe firmware update from SD card and possibility to go back to original close-source firmware).

buildroot/share/PlatformIO/scripts/mks_robin.py

@@ -0,0 +1,28 @@
+Import("env")
+
+# Relocate firmware from 0x08000000 to 0x08007000
+env['CPPDEFINES'].remove(("VECT_TAB_ADDR", 134217728))
+env['CPPDEFINES'].append(("VECT_TAB_ADDR", "0x08007000"))
+env.Replace(LDSCRIPT_PATH="buildroot/share/PlatformIO/ldscripts/mks_robin.ld")
+
+# Encrypt ${PROGNAME}.bin and save it as 'Robin.bin'
+def encrypt(source, target, env):
+    import os
+
+    key = [0xA3, 0xBD, 0xAD, 0x0D, 0x41, 0x11, 0xBB, 0x8D, 0xDC, 0x80, 0x2D, 0xD0, 0xD2, 0xC4, 0x9B, 0x1E, 0x26, 0xEB, 0xE3, 0x33, 0x4A, 0x15, 0xE4, 0x0A, 0xB3, 0xB1, 0x3C, 0x93, 0xBB, 0xAF, 0xF7, 0x3E]
+
+    firmware = open(target[0].path, "rb")
+    robin = open(target[0].dir.path +'/Robin.bin', "wb")
+    length = os.path.getsize(target[0].path)
+    position = 0
+    try:
+        while position < length:
+            byte = firmware.read(1)
+            if position >= 320 and position < 31040:
+                byte = chr(ord(byte) ^ key[position & 31])
+            robin.write(byte)
+            position += 1
+    finally:
+        firmware.close()
+        robin.close()
+env.AddPostAction("$BUILD_DIR/${PROGNAME}.bin", encrypt);