stmmac: cleanup dead dependencies on STMMAC_PLATFORM and STMMAC_ETH in Kconfig

stmmac: cleanup dead dependencies on STMMAC_PLATFORM and STMMAC_ETH in Kconfig

There are already 'if STMMAC_ETH' and 'STMMAC_PLATFORM'
conditions wrapping these config options, making the
'depends on' statements duplicate dependencies (dead code).

I propose leaving the outer 'if STMMAC_PLATFORM...endif' and
'if STMMAC_ETH...endif' conditions, and removing the
individual 'depends on' statements.

This dead code was found by kconfirm, a static analysis tool for Kconfig.

Signed-off-by: Julian Braha <julianbraha@gmail.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/20260402145858.240231-1-julianbraha@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>