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/zynq_zc770_xm011_defconfig b/configs/zynq_zc770_xm011_defconfig
index 84f46a7..6d377e9 100644
--- a/configs/zynq_zc770_xm011_defconfig
+++ b/configs/zynq_zc770_xm011_defconfig
@@ -10,6 +10,8 @@
 # CONFIG_SPL_FS_FAT is not set
 CONFIG_DEBUG_UART=y
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SYS_CUSTOM_LDSCRIPT=y
+CONFIG_SYS_LDSCRIPT="arch/arm/mach-zynq/u-boot.lds"
 CONFIG_FIT=y
 CONFIG_FIT_SIGNATURE=y
 CONFIG_FIT_VERBOSE=y