arm: discard relocation entries for secure text

The code such as PSCI in section named secure is bundled with
u-boot image, and when bootm, the code will be copied to their
runtime address same to compliation/linking address -
CONFIG_ARMV7_SECURE_BASE.

When compile the PSCI code and link it into the u-boot image,
there will be relocation entries in .rel.dyn section for PSCI.
Actually, we do not needs these relocation entries.

If still keep the relocation entries in .rel.dyn section,
r0 at line 103 and 106 in arch/arm/lib/relocate.S may be an invalid
address which may not support read/write for one SoC.
102         /* relative fix: increase location by offset */
103         add     r0, r0, r4
104         ldr     r1, [r0]
105         add     r1, r1, r4
106         str     r1, [r0]

So discard them to avoid touching the relocation entry in
arch/arm/lib/relocate.S.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Tom Warren <twarren@nvidia.com>
Cc: York Sun <yorksun@freescale.com>
Cc: Hans De Goede <hdegoede@redhat.com>
Cc: Ian Campbell <ijc@hellion.org.uk>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Tom Rini <trini@konsulko.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Stefano Babic <sbabic@denx.de>
Acked-by: Albert ARIBAUD <albert.u.boot@aribaud.net>

arch/arm/cpu/u-boot.lds

@@ -14,6 +14,23 @@ OUTPUT_ARCH(arm)
 ENTRY(_start)
 SECTIONS
 {
+	/*
+	 * Discard the relocation entries for secure text.
+	 * The secure code is bundled with u-boot image, so there will
+	 * be relocations entries for the secure code, since we use
+	 * "-mword-relocations" to compile and "-pie" to link into the
+	 * final image. We do not need the relocation entries for secure
+	 * code, because secure code will not be relocated, it only needs
+	 * to be copied from loading address to CONFIG_ARMV7_SECURE_BASE,
+	 * which is the linking and running address for secure code.
+	 * If keep the relocation entries in .rel.dyn section,
+	 * "relocation offset + linking address" may locates into an
+	 * address that is reserved by SoC, then will trigger data abort.
+	 *
+	 * The reason that move .rel._secure at the beginning, is to
+	 * avoid hole in the final image.
+	 */
+	/DISCARD/ : { *(.rel._secure*) }
 	. = 0x00000000;
 
 	. = ALIGN(4);