Change in coreboot[master]: vendor: mediatek: Add mediatek mt8192 dram initialization code

[Xi Chen (Code Review)]

Attention is currently required from: Hung-Te Lin, Nico Huber, Martin Roth, Paul Menzel, Julius Werner, Angel Pons, Yu-Ping Wu.
Xi Chen has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/50294 )

Change subject: vendor: mediatek: Add mediatek mt8192 dram initialization code
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Patch Set 18:

(1 comment)

File src/vendorcode/mediatek/Kconfig:

https://review.coreboot.org/c/coreboot/+/50294/comment/02e30839_c586a315 
PS16, Line 3: config DEBUG_DRAM
            : 	bool "Output verbose DRAM related debug messages"
            : 	default y
            : 	help
            : 	  This option enables additional DRAM related debug messages.
> Thanks for all your advice. Reuse DEBUG_RAM_SETUP is very good. […]

@hung-te: CB:51125 ps11 has changed dramc_dbg to mediatek common header file.
          Besides of mt8192, mt8173 and mt8183 both use the common dramc_dbg macro now.  
   Also, MEMORY_TEST config is moved to soc/mediatek/common/Kconfig, which is shared by all MTK SOCs.