Some eMMC chips may need the RST_n_FUNCTION bit set to a non-zero value
in order for warm reset of the system to work.  Details on this being
required will be part of the eMMC datasheet.  Also add using this
command to the dra7xx README.

* Whitespace fix by panto

Signed-off-by: Tom Rini <trini@ti.com>
Acked-by: Pantelis Antoniou <panto@antoniou-consulting.com>