net/mlx5: Kconfig: convert imply usage to weak dependency

MLX5_CORE uses the 'imply' keyword to depend on VXLAN, PTP_1588_CLOCK,
MLXFW and PCI_HYPERV_INTERFACE.

This was useful to force vxlan, ptp, etc.. to be reachable to mlx5
regardless of their config states.

Due to the changes in the cited commit below, the semantics of 'imply'
was changed to not force any restriction on the implied config.

As a result of this change, the compilation of MLX5_CORE=y and VXLAN=m
would result in undefined references, as VXLAN now would stay as 'm'.

To fix this we change MLX5_CORE to have a weak dependency on
these modules/configs and make sure they are reachable, by adding:
depend on symbol || !symbol.

For example: VXLAN=m MLX5_CORE=y, this will force MLX5_CORE to m

Fixes: def2fbff ("kconfig: allow symbols implied by y to become m")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nicolas Pitre <nico@fluxnic.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Reported-by: Randy Dunlap <rdunlap@infradead.org>