cbfstool: Add helper function buffer_from_file_aligned_size

This change adds a helper function `buffer_from_file_aligned_size`
that loads a file into memory buffer by creating a memory buffer of
size rounded up to the provided `size_granularity` parameter.

BUG=b:189177186,b:189167923

Change-Id: Iad3430d476abcdad850505ac50e36cd5d5deecb4
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55989
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

util/cbfstool/common.h

@@ -132,6 +132,11 @@ int buffer_create(struct buffer *buffer, size_t size, const char *name);
 /* Loads a file into memory buffer. Returns 0 on success, otherwise non-zero. */
 int buffer_from_file(struct buffer *buffer, const char *filename);
 
+/* Loads a file into memory buffer (with buffer size rounded up to a multiple of
+   size_granularity). Returns 0 on success, otherwise non-zero. */
+int buffer_from_file_aligned_size(struct buffer *buffer, const char *filename,
+				  size_t size_granularity);
+
 /* Writes memory buffer content into file.
  * Returns 0 on success, otherwise non-zero. */
 int buffer_write_file(struct buffer *buffer, const char *filename);