board: xilinx: Add support for user configurable boot script offset

Currently "script_offset_f" env variable is hardcoded, this variable
specifies from which offset of the flash boot.scr should be read/write.
As flashes are of different sizes having a fixed offset makes it
difficult to load other images into the flash which may overwrite the
boot script or cannot utilize the full memory. This current fix
creates a new config "CONFIG_BOOT_SCRIPT_OFFSET" which holds the
offset address, overwrites the "script_offset_f" variable.
Also removed existing variable with default values, as the default
values are held by CONFIG_BOOT_SCRIPT_OFFSET

Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

include/configs/xilinx_versal.h

@@ -92,7 +92,6 @@
 	"kernel_size_r=0x10000000\0" \
 	"scriptaddr=0x20000000\0" \
 	"ramdisk_addr_r=0x02100000\0" \
-	"script_offset_f=0x7F80000\0" \
 	"script_size_f=0x80000\0"
 
 #if defined(CONFIG_MMC_SDHCI_ZYNQ)

include/configs/xilinx_zynqmp.h

@@ -114,7 +114,6 @@
 	"kernel_addr_r=0x18000000\0" \
 	"scriptaddr=0x20000000\0" \
 	"ramdisk_addr_r=0x02100000\0" \
-	"script_offset_f=0x3e80000\0" \
 	"script_size_f=0x80000\0" \
 
 #if defined(CONFIG_MMC_SDHCI_ZYNQ)

include/configs/zynq-common.h

@@ -194,7 +194,6 @@
 	"fdt_high=0x20000000\0"		\
 	"initrd_high=0x20000000\0"	\
 	"scriptaddr=0x20000\0"	\
-	"script_offset_f=0xFC0000\0"	\
 	"script_size_f=0x40000\0"	\
 	"fdt_addr_r=0x1f00000\0"        \
 	"pxefile_addr_r=0x2000000\0"    \