x86/bootflag: Replace open-coded parity calculation with parity8()

Refactor parity calculations to use the standard parity8() helper. This
change eliminates redundant implementations and improves code
efficiency.

[ ubizjak: Updated the patch to apply to the latest x86 tree. ]

Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20250227125616.2253774-1-ubizjak@gmail.com

arch/x86/kernel/bootflag.c

@@ -8,6 +8,7 @@
 #include <linux/string.h>
 #include <linux/spinlock.h>
 #include <linux/acpi.h>
+#include <linux/bitops.h>
 #include <asm/io.h>
 
 #include <linux/mc146818rtc.h>
@@ -20,25 +21,12 @@
 
 int sbf_port __initdata = -1;	/* set via acpi_boot_init() */
 
-static bool __init parity(u8 v)
-{
-	int x = 0;
-	int i;
-
-	for (i = 0; i < 8; i++) {
-		x ^= (v & 1);
-		v >>= 1;
-	}
-
-	return !!x;
-}
-
 static void __init sbf_write(u8 v)
 {
 	unsigned long flags;
 
 	if (sbf_port != -1) {
-		if (!parity(v))
+		if (!parity8(v))
 			v ^= SBF_PARITY;
 
 		printk(KERN_INFO "Simple Boot Flag at 0x%x set to 0x%x\n",
@@ -69,7 +57,7 @@ static bool __init sbf_value_valid(u8 v)
 {
 	if (v & SBF_RESERVED)		/* Reserved bits */
 		return false;
-	if (!parity(v))
+	if (!parity8(v))
 		return false;
 
 	return true;