common: Move relocate_code() to init.h

This is an init function so move it out of the common header. Avoid using
the typedef so that we don't have to include the global_data header file.

Also tidy up the function style in comments while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S
index 1a55b7d..f3dccdb 100644
--- a/arch/riscv/cpu/start.S
+++ b/arch/riscv/cpu/start.S
@@ -217,7 +217,7 @@
 #endif
 
 /*
- * void relocate_code (addr_sp, gd, addr_moni)
+ * void relocate_code(addr_sp, gd, addr_moni)
  *
  * This "function" does not return, instead it continues in RAM
  * after relocating the monitor code.