U-Boot: Add a ppc ldscript

* mostly copied from the ARM one

src/system/ldscripts/ppc/boot_loader_u-boot.ld

@@ -0,0 +1,63 @@
+OUTPUT_FORMAT("elf32-powerpc", "elf32-powerpc", "elf32-powerpc")
+OUTPUT_ARCH(powerpc)
+
+ENTRY(_start)
+SECTIONS
+{
+	. = BOARD_LOADER_BASE;
+
+	/* text/read-only data */
+	.text :	{ *(.text .gnu.linkonce.t.*) }
+
+	. = ALIGN(0x4);
+	__ctor_list = .;
+	.ctors : { *(.ctors) *(.init_array) }
+	__ctor_end = .;
+
+	.rodata : { *(.rodata .rodata.*) }
+
+	/* writable data  */
+	. = ALIGN(0x1000);
+	__data_start = .;
+	.data : { *(.data .gnu.linkonce.d.*) }
+
+	/* uninitialized data (in same segment as writable data) */
+	__bss_start = .;
+	.bss : { *(.bss) }
+
+	. = ALIGN(0x1000);
+	_end = . ;
+
+  /* Stabs debugging sections.  */
+  .stab 0 : { *(.stab) }
+  .stabstr 0 : { *(.stabstr) }
+  /* DWARF debug sections.
+     Symbols in the DWARF debugging sections are relative to the beginning
+     of the section so we begin them at 0.  */
+  /* DWARF 1 */
+  .debug          0 : { *(.debug) }
+  .line           0 : { *(.line) }
+  /* GNU DWARF 1 extensions */
+  .debug_srcinfo  0 : { *(.debug_srcinfo) }
+  .debug_sfnames  0 : { *(.debug_sfnames) }
+  /* DWARF 1.1 and DWARF 2 */
+  .debug_aranges  0 : { *(.debug_aranges) }
+  .debug_pubnames 0 : { *(.debug_pubnames) }
+  /* DWARF 2 */
+  .debug_info     0 : { *(.debug_info) }
+  .debug_abbrev   0 : { *(.debug_abbrev) }
+  .debug_line     0 : { *(.debug_line) }
+  .debug_frame    0 : { *(.debug_frame) }
+  .debug_str      0 : { *(.debug_str) }
+  .debug_loc      0 : { *(.debug_loc) }
+  .debug_macinfo  0 : { *(.debug_macinfo) }
+  /* SGI/MIPS DWARF 2 extensions */
+  .debug_weaknames 0 : { *(.debug_weaknames) }
+  .debug_funcnames 0 : { *(.debug_funcnames) }
+  .debug_typenames 0 : { *(.debug_typenames) }
+  .debug_varnames  0 : { *(.debug_varnames) }
+  /* These must appear regardless of  .  */
+
+	/* Strip unnecessary stuff */
+/*	/DISCARD/ : { *(.comment .note .eh_frame .dtors .stab .stabstr .debug*) }*/
+}