image: Add support for placing crypto_algo in linker lists

The purpose of this change is to enable crypto algorithms to be placed
in linker lists, rather than be declared as a static array. The goal
is to remove the crypto_algos array in a subsequent patch.

Create a new linker list named "cryptos", and search it when
image_get_crypto_algo() is invoked.

NOTE that adding support for manual relocation of crypto_algos within
linker lists is beyond the scope of this patch.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>