clk: sifive: fu540-prci: Release ethernet clock reset

U-Boot ethernet works with FSBL flow where releasing ethernet clock
reset is part of FSBL itself but with the SPL, We need to release
ethernet clock reset explicitly for U-Boot proper. With this change
Release ethernet clock reset code in FSBL might not be needed or
unaffected.

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>