highmem: add kernel-doc for memcpy_*_folio()

This was inadvertently skipped when adding the new functions.

Link: https://lkml.kernel.org/r/20240124181217.1761674-1-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/highmem.h

@@ -439,6 +439,13 @@ static inline void memzero_page(struct page *page, size_t offset, size_t len)
 	kunmap_local(addr);
 }
 
+/**
+ * memcpy_from_folio - Copy a range of bytes from a folio.
+ * @to: The memory to copy to.
+ * @folio: The folio to read from.
+ * @offset: The first byte in the folio to read.
+ * @len: The number of bytes to copy.
+ */
 static inline void memcpy_from_folio(char *to, struct folio *folio,
 		size_t offset, size_t len)
 {
@@ -460,6 +467,13 @@ static inline void memcpy_from_folio(char *to, struct folio *folio,
 	} while (len > 0);
 }
 
+/**
+ * memcpy_to_folio - Copy a range of bytes to a folio.
+ * @folio: The folio to write to.
+ * @offset: The first byte in the folio to store to.
+ * @from: The memory to copy from.
+ * @len: The number of bytes to copy.
+ */
 static inline void memcpy_to_folio(struct folio *folio, size_t offset,
 		const char *from, size_t len)
 {