arm: orion5x: finish moving SoC to mach-orion5x

The SPL linker script had been left in arch/$(ARCH)/cpu/$(CPU)/$(SOC);
therefore move it to the already-established arch/$(ARCH)/mach-$(SOC)
location.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>

configs/edminiv2_defconfig

 CONFIG_ARM=y
 CONFIG_ARCH_CPU_INIT=y
 CONFIG_ARCH_ORION5X=y
-CONFIG_SPL_LDSCRIPT="arch/arm/cpu/arm926ejs/orion5x/u-boot-spl.lds"
+CONFIG_SPL_LDSCRIPT="arch/arm/mach-orion5x/u-boot-spl.lds"
 CONFIG_SYS_TEXT_BASE=0x00800000
 CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_SPL_LIBGENERIC_SUPPORT=y