mips: add __image_copy_len for SPL linker script

This patch adds __image_copy_len needed by TPL of MT7621 SoC.
The __image_copy_len represents the binary blob size of both SPL/TPL
binaries. To achieve this, __text_start/end are added for calculation.

Reviewed-by: Daniel Schwierzeck <[email protected]>
Signed-off-by: Weijie Gao <[email protected]>

Author: hackpascal

Diff for: arch/mips/cpu/u-boot-spl.lds

@@ -13,7 +13,9 @@ SECTIONS
 
 	. = ALIGN(4);
 	.text : {
+		__text_start = .;
 		*(.text*)
+		__text_end = .;
 	} > .spl_mem
 
 	. = ALIGN(4);
@@ -36,6 +38,7 @@ SECTIONS
 
 	. = ALIGN(4);
 	__image_copy_end = .;
+	__image_copy_len = __image_copy_end - __text_start;
 
 	_image_binary_end = .;