Input: pxa27x_keypad - enable rotary encoders and direct keys

1. Rotary encoder events can be configured either as relative events
   as the legacy code does or as any specified key code, this is
   useful on some platform which uses the rotary keys as
   KEY_{UP/DOWN/LEFT/RIGHT}

2. Add support for direct keys, the corresponding keycodes for each
   direct key can now be specified within the platform data

3. Remove the direct/rotary key detection code from the IRQ handler
   to dedicated functions to improve readability

Signed-off-by: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>