doc: imx: Improve i.MX documentation naming

There is no need to have README in all i.MX documents name.
Remove README from i.MX docs name and add .txt file extension.

Signed-off-by: Breno Lima <breno.lima@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>

diff --git a/doc/imx/common/README.imx25 b/doc/imx/common/imx25.txt
similarity index 100%
rename from doc/imx/common/README.imx25
rename to doc/imx/common/imx25.txt

diff --git a/doc/imx/common/README.imx27 b/doc/imx/common/imx27.txt
similarity index 100%
rename from doc/imx/common/README.imx27
rename to doc/imx/common/imx27.txt

diff --git a/doc/imx/common/README.imx5 b/doc/imx/common/imx5.txt
similarity index 100%
rename from doc/imx/common/README.imx5
rename to doc/imx/common/imx5.txt

diff --git a/doc/imx/common/README.imx6 b/doc/imx/common/imx6.txt
similarity index 100%
rename from doc/imx/common/README.imx6
rename to doc/imx/common/imx6.txt

diff --git a/doc/imx/common/README.mxs b/doc/imx/common/mxs.txt
similarity index 100%
rename from doc/imx/common/README.mxs
rename to doc/imx/common/mxs.txt

diff --git a/doc/imx/misc/README.sdp b/doc/imx/misc/sdp.txt
similarity index 100%
rename from doc/imx/misc/README.sdp
rename to doc/imx/misc/sdp.txt

diff --git a/doc/imx/mkimage/README.imximage b/doc/imx/mkimage/imximage.txt
similarity index 100%
rename from doc/imx/mkimage/README.imximage
rename to doc/imx/mkimage/imximage.txt

diff --git a/doc/imx/mkimage/README.mxsimage b/doc/imx/mkimage/mxsimage.txt
similarity index 100%
rename from doc/imx/mkimage/README.mxsimage
rename to doc/imx/mkimage/mxsimage.txt