rust: ptr: add const_align_up()

Add const_align_up() to kernel::ptr as the const-compatible equivalent
of Alignable::align_up().

Suggested-by: Danilo Krummrich <dakr@kernel.org>
Suggested-by: Gary Guo <gary@garyguo.net>
Suggested-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260326013902.588242-17-jhubbard@nvidia.com
[ Adjusted imports style. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: johnhubbard

rust/kernel/ptr.rs

@@ -225,3 +225,32 @@ macro_rules! impl_alignable_uint {
 }
 
 impl_alignable_uint!(u8, u16, u32, u64, usize);
+
+/// Aligns `value` up to `align`.
+///
+/// This is the const-compatible equivalent of [`Alignable::align_up`].
+///
+/// Returns [`None`] on overflow.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::{
+///     ptr::{
+///         const_align_up,
+///         Alignment, //
+///     },
+///     sizes::SZ_4K, //
+/// };
+///
+/// assert_eq!(const_align_up(0x4f, Alignment::new::<16>()), Some(0x50));
+/// assert_eq!(const_align_up(0x40, Alignment::new::<16>()), Some(0x40));
+/// assert_eq!(const_align_up(1, Alignment::new::<SZ_4K>()), Some(SZ_4K));
+/// ```
+#[inline(always)]
+pub const fn const_align_up(value: usize, align: Alignment) -> Option<usize> {
+    match value.checked_add(align.as_usize() - 1) {
+        Some(v) => Some(v & align.mask()),
+        None => None,
+    }
+}