spi: Kconfig: Mark LPC32XX_SSP as DEPRECATED

Mark LPC32XX_SSP as DEPRECATED, this so the resulting build shows
warning for deprecated configuration enabled and associated code
will remove in v2019.07 release.

Cc: Albert ARIBAUD <albert.aribaud@3adev.fr>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Acked-by: Sylvain Lemieux <slemieux@tycoint.com>
[trini: Switch to DEPRECATED]
Signed-off-by: Tom Rini <trini@konsulko.com>