docs(changelog): add subsection for uSDHC

Add a new subsection for the NXP uSDHC driver, placed under the
drivers/imx/usdhc folder. Choose 'mmc' over 'usdhc' due to the length
advantage. This will leave more space for the commit titles.

Change-Id: Ie024272c201b7cabf231c78143f4179c885020a5
Signed-off-by: Ghennadi Procopciuc <ghennadi.procopciuc@nxp.com>
1 file changed