Fix typo: IMAGEDEF → IMAGE_DEF, as it is defined in the datasheet (#2589)

src/rp2_common/pico_crt0/rp2350/memmap_copy_to_ram.ld

@@ -35,7 +35,7 @@ SECTIONS
 {
        /* On Arm, the bootrom expects a VT at the start of the
        image by default; on RISC-V, the default is to enter the image at its
-       lowest address, so an IMAGEDEF item is required to specify the
+       lowest address, so an IMAGE_DEF item is required to specify the
        nondefault entry point. */
 
     .flash_begin : {

src/rp2_common/pico_crt0/rp2350/memmap_no_flash.ld

@@ -35,7 +35,7 @@ SECTIONS
     /* Note unlike RP2040, we start the image with a vector table even for
        NO_FLASH builds. On Arm, the bootrom expects a VT at the start of the
        image by default; on RISC-V, the default is to enter the image at its
-       lowest address, so an IMAGEDEF item is required to specify the
+       lowest address, so an IMAGE_DEF item is required to specify the
        nondefault entry point. */
 
     .text : {