wordpart.h: Add REPEAT_BYTE_U32()

In some cases it's necessary to replicate a byte across a u32 value, for
which REPEAT_BYTE() would be helpful. Currently this requires explicit
masking of the result to avoid sparse warnings, as e.g.

    (u32)REPEAT_BYTE(0xa0))

... will result in a warning:

    cast truncates bits from constant value (a0a0a0a0a0a0a0a0 becomes a0a0a0a0)

Add a new REPEAT_BYTE_U32() which does the necessary masking internally,
so that we don't need to duplicate this for every usage.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20240617111841.2529370-2-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>

Author: mrutland-arm

include/linux/wordpart.h

@@ -39,6 +39,14 @@
  */
 #define REPEAT_BYTE(x)	((~0ul / 0xff) * (x))
 
+/**
+ * REPEAT_BYTE_U32 - repeat the value @x multiple times as a u32 value
+ * @x: value to repeat
+ *
+ * NOTE: @x is not checked for > 0xff; larger values produce odd results.
+ */
+#define REPEAT_BYTE_U32(x)	lower_32_bits(REPEAT_BYTE(x))
+
 /* Set bits in the first 'n' bytes when loaded from memory */
 #ifdef __LITTLE_ENDIAN
 #  define aligned_byte_mask(n) ((1UL << 8*(n))-1)