Changes in commit 533eb415 ("arm/aspeed: actually check RAM size")
introduced a 'valid_ram_sizes' array which can be used to compute the
associated bit field value encoding the RAM size. The field is simply
the index of the array.

Reviewed-by: Joel Stanley <joel@jms.id.au>
Message-Id: <20200819100956.2216690-19-clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>