[efi] Fix linker script for ld 2.17.50.0.9

Some versions of ld choke on the "AT ( _xxx_lma )" in efi.lds with an
error saying "nonconstant expression for load base".  Since these were
only explicitly setting the LMA to the address that it would have had
anyway, they can be safely omitted.

src/arch/i386/scripts/efi.lds

      *
      */
 
-    .prefix : AT ( _prefix_lma ) {
+    .prefix : {
 	_prefix = .;
 	*(.prefix)
 	*(.prefix.*)
      */
 
     . = ALIGN ( _max_align );
-    .text : AT ( _text_lma ) {
+    .text : {
 	_text = .;
 	*(.text)
 	*(.text.*)
      */
 
     . = ALIGN ( _max_align );
-    .rodata : AT ( _rodata_lma ) {
+    .rodata : {
 	_rodata = .;
 	*(.rodata)
 	*(.rodata.*)
      */
 
     . = ALIGN ( _max_align );
-    .data : AT ( _data_lma ) {
+    .data : {
 	_data = .;
 	*(.data)
 	*(.data.*)
      */
 
     . = ALIGN ( _max_align );
-    .bss : AT ( _bss_lma ) {
+    .bss : { 
 	_bss = .;
 	/* EFI seems to not support proper bss sections */
 	_mbss = .;
      */
 
     . = ALIGN ( _max_align );
-    .reloc : AT ( _reloc_lma ) {
+    .reloc : {
 	_reloc = .;
 	/* Provide some dummy contents to force ld to include this
 	 * section.  It will be created by the efilink utility.