net: stmmac: Use str_enabled_disabled() helper

net: stmmac: Use str_enabled_disabled() helper

As kernel test robot reported, the following warning occurs:

cocci warnings: (new ones prefixed by >>)
>> drivers/net/ethernet/stmicro/stmmac/dwmac1000_core.c:582:6-8: opportunity for str_enabled_disabled(on)

Replace ternary (condition ? "enabled" : "disabled") with
str_enabled_disabled() from string_choices.h to improve readability,
maintain uniform string usage, and reduce binary size through linker
deduplication.

Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
Link: https://patch.msgid.link/20250217155833.3105775-1-eleanor15x@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>