c6x: normalize global variables exported by vmlinux.lds

Normalize global variables exported by vmlinux.lds to conform usage
guidelines from include/asm-generic/sections.h.

Use _text to mark the start of the kernel image including the head text,
and _stext to mark the start of the .text section.

This patch also fixes possible bugs due to current address layout that
[__init_begin, __init_end] is a sub-range of [_stext, _etext] and pages
within range [__init_begin, __init_end] will be freed by free_initmem().
Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/c6x/kernel/vmlinux.lds.S

@@ -54,16 +54,15 @@ SECTIONS
 	}
 
 	. = ALIGN(PAGE_SIZE);
+	__init_begin = .;
 	.init :
 	{
-		_stext = .;
 		_sinittext = .;
 		HEAD_TEXT
 		INIT_TEXT
 		_einittext = .;
 	}
 
-	__init_begin = _stext;
 	INIT_DATA_SECTION(16)
 
 	PERCPU_SECTION(128)
@@ -74,6 +73,7 @@ SECTIONS
 	.text :
 	{
 		_text = .;
+		_stext = .;
 		TEXT_TEXT
 		SCHED_TEXT
 		LOCK_TEXT