UML: normalize global variables exported by vmlinux.lds

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

1) Use _text to mark the start of the kernel image including the head
text, and _stext to mark the start of the .text section.
2) Export mandatory global variables __bss_stop.
3) Adjust __init_begin and __init_end to avoid acrossing .text and
   .data sections.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/kernel/dyn.lds.S

@@ -14,8 +14,6 @@ SECTIONS
   __binary_start = .;
   . = ALIGN(4096);		/* Init code and data */
   _text = .;
-  _stext = .;
-  __init_begin = .;
   INIT_TEXT_SECTION(PAGE_SIZE)
 
   . = ALIGN(PAGE_SIZE);
@@ -67,6 +65,7 @@ SECTIONS
   } =0x90909090
   .plt            : { *(.plt) }
   .text           : {
+    _stext = .;
     TEXT_TEXT
     SCHED_TEXT
     LOCK_TEXT
@@ -91,7 +90,9 @@ SECTIONS
 
   #include <asm/common.lds.S>
 
+  __init_begin = .;
   init.data : { INIT_DATA }
+  __init_end = .;
 
   /* Ensure the __preinit_array_start label is properly aligned.  We
      could instead move the label definition inside the section, but
@@ -155,6 +156,7 @@ SECTIONS
    . = ALIGN(32 / 8);
   . = ALIGN(32 / 8);
   }
+   __bss_stop = .;
   _end = .;
   PROVIDE (end = .);