The status bits of register MAC_FPE_CTRL_STS are clear on read. Using
32-bit read for MAC_FPE_CTRL_STS in dwmac5_fpe_configure() and
dwmac5_fpe_send_mpacket() clear the status bits. Then the stmmac interrupt
handler missing FPE event status and leads to FPE handshaking failure and
retries.
To avoid clear status bits of MAC_FPE_CTRL_STS in dwmac5_fpe_configure()
and dwmac5_fpe_send_mpacket(), add fpe_csr to stmmac_fpe_cfg structure to
cache the control bits of MAC_FPE_CTRL_STS and to avoid reading
MAC_FPE_CTRL_STS in those methods.

Fixes: 5a558611 ("net: stmmac: support FPE link partner hand-shaking procedure")
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Jianheng Zhang <Jianheng.Zhang@synopsys.com>
Link: https://lore.kernel.org/r/CY5PR12MB637225A7CF529D5BE0FBE59CBF81A@CY5PR12MB6372.namprd12.prod.outlook.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>