mmc: sh_mobile_sdhi: remove support for sh7372

Remove documentation of support for the SH7372 (SH-Mobile AP4) from the MMC
driver. The driver itself appears to have no SH7372 specific code.

Commit edf41009 ("ARM: shmobile: sh7372 dtsi: Remove Legacy file")
removes this SoC from the kernel in v4.1.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>