aspeed: Board init functions and common configs for ast2500 based boards

Add configuration file with parameters that are very likely to be shared by
all ast2500-based boards.
Add ast2500-board.c fil

aspeed: Board init functions and common configs for ast2500 based boards

Add configuration file with parameters that are very likely to be shared by
all ast2500-based boards.
Add ast2500-board.c file with the init code that is very likely to be
shared by all ast2500-based boards.
Reviewed-by: Simon Glass <sjg@chromium.org>

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