package/libssh: fix dependency on libgcrypt

package/libssh: fix dependency on libgcrypt

Since 2f89476 (package/libgpg-error: bump to version 1.23), libssh has
inherited the dependency from libgcrypt (propagated from libgpg-error).

However, since libssh can use either openssl or libgcrypt as a backend,
the dependency should be relaxed when openssl is available.

But the test is broken and inverted: it will make libssh unavailable as
soon as openssl is enabled.

This in itself is already incorrect, but that can cause further issues,
as some packages (e.g. Kodi) will select (indirectly) openssl, and has
an option to select libssh; enabling that option causes unmet direct
dependencies of libssh:

    warning: (BR2_PACKAGE_KODI_LIBSSH) selects BR2_PACKAGE_LIBSSH which
    has unmet direct dependencies (BR2_USE_MMU && !BR2_STATIC_LIBS &&
    BR2_TOOLCHAIN_HAS_THREADS && BR2_PACKAGE_LIBGPG_ERROR_ARCH_SUPPORTS
    && !BR2_PACKAGE_OPENSSL)

Fix this dependency by doing what other similar packages do: select
openssl if the other crypto backend (here libgcrypt) is not enabled.
This also allows us to drop the propagated dependency on the arch
condition.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Cc: Jörg Krause <joerg.krause@embedded.rocks>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Cc: Romain Naour <romain.naour@openwide.fr>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>