board: variscite: Remove <common.h> and add needed includes

Remove <common.h> from this board vendor directory and when needed
add missing include files directly.

Signed-off-by: Tom Rini <trini@konsulko.com>
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Cc: Parthiban Nallathambi <parthitce@gmail.com>
Cc: Hugo Villeneuve <hvilleneuve@dimonoff.com>