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 <[e-mail]>
Cc: Jeff Dike <[e-mail]>
Cc: Richard Weinberger <[e-mail]>
Cc: Al Viro <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/um/include/asm/common.lds.S

···
 	*(.uml.initcall.init)
 	__uml_initcall_end = .;
   }
-  __init_end = .;
 
   SECURITY_INIT
 

arch/um/kernel/dyn.lds.S

···
   __binary_start = .;
   . = ALIGN(4096);		/* Init code and data */
   _text = .;
-  _stext = .;
-  __init_begin = .;
   INIT_TEXT_SECTION(PAGE_SIZE)
 
   . = ALIGN(PAGE_SIZE);
···
   } =0x90909090
   .plt            : { *(.plt) }
   .text           : {
+    _stext = .;
     TEXT_TEXT
     SCHED_TEXT
     LOCK_TEXT
···
 
   #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
···
    . = ALIGN(32 / 8);
   . = ALIGN(32 / 8);
   }
+   __bss_stop = .;
   _end = .;
   PROVIDE (end = .);
 

arch/um/kernel/uml.lds.S

···
   . = START + SIZEOF_HEADERS;
 
   _text = .;
-  _stext = .;
-  __init_begin = .;
   INIT_TEXT_SECTION(0)
   . = ALIGN(PAGE_SIZE);
 
   .text      :
   {
+    _stext = .;
     TEXT_TEXT
     SCHED_TEXT
     LOCK_TEXT
···
 
   #include <asm/common.lds.S>
 
+  __init_begin = .;
   init.data : { INIT_DATA }
+  __init_end = .;
+
   .data    :
   {
     INIT_TASK_DATA(KERNEL_STACK_SIZE)
···
   PROVIDE(_bss_start = .);
   SBSS(0)
   BSS(0)
+   __bss_stop = .;
   _end = .;
   PROVIDE (end = .);