power: supply: lp8788: Make several arrays static const * const

Don't populate various read only arrays on the stack but make them
static const, making the object code smaller and saves 148 bytes
overall:

Before:
   text    data     bss     dec     hex filename
  11940    4496      64   16500    4074 lp8788-charger.o

After:
   text    data     bss     dec     hex filename
  11472    4816      64   16352    3fe0 lp8788-charger.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>