Input: imagis - use FIELD_GET where applicable

Instead of manually extracting certain bits from registers with binary
ANDs and shifts, the FIELD_GET macro can be used. With this in mind, the
*_SHIFT macros can be dropped.

Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
Link: https://lore.kernel.org/r/20240306-b4-imagis-keys-v3-1-2c429afa8420@skole.hr
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>