devres: Align data[] to ARCH_KMALLOC_MINALIGN

Initially we bumped into problem with 32-bit aligned atomic64_t
on ARC, see [1]. And then during quite lengthly discussion Peter Z.
mentioned ARCH_KMALLOC_MINALIGN which IMHO makes perfect sense.
If allocation is done by plain kmalloc() obtained buffer will be
ARCH_KMALLOC_MINALIGN aligned and then why buffer obtained via
devm_kmalloc() should have any other alignment?

This way we at least get the same behavior for both types of
allocation.

[1] http://lists.infradead.org/pipermail/linux-snps-arc/2018-July/004009.html
[2] http://lists.infradead.org/pipermail/linux-snps-arc/2018-July/004036.html

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Greg KH <greg@kroah.com>
Cc: <stable@vger.kernel.org> # 4.8+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/devres.c

@@ -26,8 +26,14 @@ struct devres_node {
 
 struct devres {
  struct devres_node node;
- /* -- 3 pointers */
- unsigned long long data[]; /* guarantee ull alignment */
+ /*
+ * Some archs want to perform DMA into kmalloc caches
+ * and need a guaranteed alignment larger than
+ * the alignment of a 64-bit integer.
+ * Thus we use ARCH_KMALLOC_MINALIGN here and get exactly the same
+ * buffer alignment as if it was allocated by plain kmalloc().
+ */
+ u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];
 };
 
 struct devres_group {