configs: Migrate CONFIG_SYS_LDSCRIPT to Kconfig

In order to migrate this symbol to Kconfig introduce a new symbol to
guard it, CONFIG_SYS_CUSTOM_LDSCRIPT.  When that is set we can then
provide the exact final location o the script.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/topic_miamilite_defconfig b/configs/topic_miamilite_defconfig
index ae65f9c..a0b016c 100644
--- a/configs/topic_miamilite_defconfig
+++ b/configs/topic_miamilite_defconfig
@@ -11,6 +11,8 @@
 CONFIG_BOOT_INIT_FILE="board/topic/zynq/zynq-topic-miamilite/ps7_regs.txt"
 CONFIG_DEBUG_UART=y
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SYS_CUSTOM_LDSCRIPT=y
+CONFIG_SYS_LDSCRIPT="arch/arm/mach-zynq/u-boot.lds"
 CONFIG_BOOTDELAY=0
 CONFIG_SPL_STACK_R=y
 CONFIG_SPL_SPI_LOAD=y