efi/gop: Use helper macros for find_bits

Use the __ffs/__fls macros to calculate the position and size of the
mask.

Correct type of mask to u32 instead of unsigned long.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200320020028.1936003-9-nivedita@alum.mit.eduSigned-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/gop.c

@@ -5,6 +5,7 @@
  *
  * ----------------------------------------------------------------------- */
 
+#include <linux/bitops.h>
 #include <linux/efi.h>
 #include <linux/screen_info.h>
 #include <asm/efi.h>
@@ -12,27 +13,16 @@
 
 #include "efistub.h"
 
-static void find_bits(unsigned long mask, u8 *pos, u8 *size)
+static void find_bits(u32 mask, u8 *pos, u8 *size)
 {
-	u8 first, len;
-
-	first = 0;
-	len = 0;
-
-	if (mask) {
-		while (!(mask & 0x1)) {
-			mask = mask >> 1;
-			first++;
-		}
-
-		while (mask & 0x1) {
-			mask = mask >> 1;
-			len++;
-		}
+	if (!mask) {
+		*pos = *size = 0;
+		return;
 	}
 
-	*pos = first;
-	*size = len;
+	/* UEFI spec guarantees that the set bits are contiguous */
+	*pos  = __ffs(mask);
+	*size = __fls(mask) - *pos + 1;
 }
 
 static void