[Bluetooth] Let BT_HIDP depend on INPUT

This patch lets BT_HIDP depend on instead of select INPUT. This fixes
the following warning during an s390 build:

net/bluetooth/hidp/Kconfig:4:warning: 'select' used by config symbol
'BT_HIDP' refer to undefined symbol 'INPUT'

A dependency on INPUT also implies !S390 (and therefore makes the
explicit dependency obsolete) since INPUT is not available on s390.

The practical difference should be nearly zero, since INPUT is always
set to y unless EMBEDDED=y (or S390=y).

Signed-off-by: Adrian Bunk <bunk@stusta.de>