spi: Zap lpc32xx_ssp driver-related code

lpc32xx_ssp driver is deprecated, no active updates
and no board user, hence dropped the same.

Cc: Vladimir Zapolskiy <vz@mleia.com>
Cc: Albert ARIBAUD <albert.aribaud@3adev.fr>
Cc: Tom Rini <trini@konsulko.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>