Blackfin: rename bootm.c to boot.c

The boot file contains functions for more than just "bootm", so rename it
accordingly.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/lib_blackfin/Makefile b/lib_blackfin/Makefile
index 3f69770..fee0fda 100644
--- a/lib_blackfin/Makefile
+++ b/lib_blackfin/Makefile
@@ -37,7 +37,7 @@
 SOBJS-y	+= memset.o
 
 COBJS-y	+= board.o
-COBJS-y	+= bootm.o
+COBJS-y	+= boot.o
 COBJS-y	+= cache.o
 COBJS-y	+= muldi3.o
 COBJS-y	+= post.o