staging: board: Fix uninitialized spinlock when attaching genpd

On Armadillo-800-EVA with CONFIG_DEBUG_SPINLOCK=y:

    BUG: spinlock bad magic on CPU#0, swapper/1
     lock: lcdc0_device+0x10c/0x308, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
    CPU: 0 PID: 1 Comm: swapper Not tainted 5.11.0-rc5-armadillo-00036-gbbca04be7a80-dirty #287
    Hardware name: Generic R8A7740 (Flattened Device Tree)
    [<c010c3c8>] (unwind_backtrace) from [<c010a49c>] (show_stack+0x10/0x14)
    [<c010a49c>] (show_stack) from [<c0159534>] (do_raw_spin_lock+0x20/0x94)
    [<c0159534>] (do_raw_spin_lock) from [<c040858c>] (dev_pm_get_subsys_data+0x8c/0x11c)
    [<c040858c>] (dev_pm_get_subsys_data) from [<c05fbcac>] (genpd_add_device+0x78/0x2b8)
    [<c05fbcac>] (genpd_add_device) from [<c0412db4>] (of_genpd_add_device+0x34/0x4c)
    [<c0412db4>] (of_genpd_add_device) from [<c0a1ea74>] (board_staging_register_device+0x11c/0x148)
    [<c0a1ea74>] (board_staging_register_device) from [<c0a1eac4>] (board_staging_register_devices+0x24/0x28)

of_genpd_add_device() is called before platform_device_register(), as it
needs to attach the genpd before the device is probed.  But the spinlock
is only initialized when the device is registered.

Fix this by open-coding the spinlock initialization, cfr.
device_pm_init_common() in the internal drivers/base code, and in the
SuperH early platform code.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/57783ece7ddae55f2bda2f59f452180bff744ea0.1626257398.git.geert+renesas@glider.beSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/board/board.c

@@ -136,6 +136,7 @@ int __init board_staging_register_clock(const struct board_staging_clk *bsc)
 static int board_staging_add_dev_domain(struct platform_device *pdev,
 					const char *domain)
 {
+	struct device *dev = &pdev->dev;
 	struct of_phandle_args pd_args;
 	struct device_node *np;
 
@@ -148,7 +149,11 @@ static int board_staging_add_dev_domain(struct platform_device *pdev,
 	pd_args.np = np;
 	pd_args.args_count = 0;
 
-	return of_genpd_add_device(&pd_args, &pdev->dev);
+	/* Initialization similar to device_pm_init_common() */
+	spin_lock_init(&dev->power.lock);
+	dev->power.early_init = true;
+
+	return of_genpd_add_device(&pd_args, dev);
 }
 #else
 static inline int board_staging_add_dev_domain(struct platform_device *pdev,