doc: update reference to README.imximage

Update reference in many files detected by
scripts/documentation-file-ref-check

README.imximage => imx/mkimage/imximage.txt

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/doc/imx/misc/sdp.txt b/doc/imx/misc/sdp.txt
index 6ea6e41..49b2812 100644
--- a/doc/imx/misc/sdp.txt
+++ b/doc/imx/misc/sdp.txt
@@ -22,7 +22,7 @@
 MFGTOOLS.
 
 The host side utilities are typically capable to interpret the i.MX
-specific image header (see doc/README.imximage). There are extensions
+specific image header (see doc/imx/mkimage/imximage.txt). There are extensions
 for imx_loader's imx_usb utility which allow to interpret the U-Boot
 specific legacy image format (see mkimage(1)). Also the U-Boot side
 support beside the i.MX specific header the U-Boot legacy header.