socfpga: agilex: fix NAND clock handling

In v2025.10, the Agilex clock driver was updated to support
clk_enable() and clk_disable() using clock-ID based bitmasks.
However, only AGILEX_NAND_CLK was implemented, while the NAND DT
node still referenced both nand and nand_x clocks.

Since AGILEX_NAND_X_CLK is not defined in the clock driver or the
clock-ID specification, clk_enable() failed during NAND probe.
As a result, the Denali NAND controller never completed
initialization.

Fix this by mapping the NAND X clock to the existing l4_mp clock
bitmask, aligning the DT expectations with the clock driver and
restoring proper NAND controller initialization.

Signed-off-by: Dinesh Maniyam <dinesh.maniyam@altera.com>
Reviewed-by: Tien Fong Chee <tien.fong.chee@altera.com>

drivers/clk/altera/clk-agilex.c

@@ -657,6 +657,7 @@ static int bitmask_from_clk_id(struct clk *clk)
 		plat->bitmask = CLKMGR_MAINPLLGRP_EN_L4MAINCLK_MASK;
 		break;
 	case AGILEX_L4_MP_CLK:
+	case AGILEX_NAND_X_CLK:
 		plat->pllgrp = CLKMGR_MAINPLL_EN;
 		plat->bitmask = CLKMGR_MAINPLLGRP_EN_L4MPCLK_MASK;
 		break;