configs: mt8512: enable fastboot and USB host related configs

Enable mtu3, xhci, tphy drivers.
Device mode: enable fastboot;
Host mode: enable USB, FAT commands, and fixed regulator,
mass storage drivers;
Due to device mode is enabled by default, comment out
the host mode config here.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>