sh: place board lowlevel_init code in the beginning of .text

Reference lowlevel_init of all supported SH2A/SH3/SH4/SH4A boards
from a shared linker script, the lowlevel_init function will be called
by a relative address.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/board/renesas/rsk7203/Makefile b/board/renesas/rsk7203/Makefile
index 16acfaf..08139a2 100644
--- a/board/renesas/rsk7203/Makefile
+++ b/board/renesas/rsk7203/Makefile
@@ -7,4 +7,4 @@
 # SPDX-License-Identifier:	GPL-2.0+
 
 obj-y	:= rsk7203.o
-obj-y	+= lowlevel_init.o
+extra-y	+= lowlevel_init.o