MIPS: Add a blank line after __HEAD

Add a blank line after __HEAD in the text section.

The __HEAD symbol was added in commit 52892ed6 ("MIPS:
Place __kernel_entry at the beginning of text section").

Signed-off-by: Rong Xu <xur@google.com>
Suggested-by: Maciej W. Rozycki <macro@orcam.me.uk>

---Changelog--
Added suggested-by.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>