Change in coreboot[master]: soc/mediatek/common/usb: Remove weak function `mtk_usb_prepare()`

[Yu-Ping Wu (Code Review)]

Attention is currently required from: Hung-Te Lin, Paul Menzel.
Yu-Ping Wu has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/59956 )

Change subject: soc/mediatek/common/usb: Remove weak function `mtk_usb_prepare()`
......................................................................

Patch Set 2:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/59956/comment/74c43b85_35bced39 
PS2, Line 9: All SoCs implement it
Kukui (mt8183) doesn't.

aarch64-elf-ld.bfd: /cb-build/coreboot-gerrit.0/chromeos/GOOGLE_KUKUI/ramstage/soc/mediatek/common/usb.o: in function `setup_usb_host':
 /home/coreboot/node-root/workspace/coreboot-gerrit/src/soc/mediatek/common/usb.c:147: undefined reference to `mtk_usb_prepare'
 /home/coreboot/node-root/workspace/coreboot-gerrit/src/soc/mediatek/common/usb.c:147:(.text.setup_usb_host+0x18): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `mtk_usb_prepare'
 make[1]: *** [src/arch/arm64/Makefile.inc:134: /cb-build/coreboot-gerrit.0/chromeos/GOOGLE_KUKUI/cbfs/fallback/ramstage.debug] Error 1