crypto: mxs-dcp - mxs-dcp is an stmp device

The mxs-dcp driver relies on the stmp_reset_block() helper function, which
is provided by CONFIG_STMP_DEVICE. This symbol is always set on MXS,
but the driver can now also be built for MXC (i.MX6), which results
in a built error if no other driver selects STMP_DEVICE:

drivers/built-in.o: In function `mxs_dcp_probe':
vf610-ocotp.c:(.text+0x3df302): undefined reference to `stmp_reset_block'

This adds the 'select', like all other stmp drivers have it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: a2712e6c ("crypto: mxs-dcp - Allow MXS_DCP to be used on MX6SL")
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>