u8800: Use correct GPIO & remove unnecessary GPIO.

U8800 does not have flash boost GPIO, neither does it have SDC4_EN_N
but rather SDC4_PWR_EN_N. This change also fixes SD card detection.
mddi_nt35582_wvga: Use internal NT35582 backlight scaling.

This change disabled PWM and uses internal NT35582 backlight changing
function. Thanks to this, backlight flickering at lower values is
solved.
u8800: Remove GPIO setting for NT35582.

No longer needed.
u8800: Fix battery voltage min-max.