ARM: dts: blanche: add support for general purpose switches

Add support  for the  general purpose  software switches  SW2 and tactile
switches SW24/25 as a virtual keyboard (like it was done with the Lager/
Koelsch boards).

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>