drm/i915: Clean up PXP Kconfig info.

During the review I focused on stop the using of the "+"
to reference the newer platforms, but I forgot that we are
in a process of making things more clear and differentiate
graphics and display versions. So, let me to clean up this
a bit. Also, we don't need any version mentioned in the
config menu entry, only in the help.

Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211015090916.82968-1-rodrigo.vivi@intel.com