swiotlb: add missing __init annotations

Impact: cleanup, reduce kernel size a bit

The current kernel build warns:

    WARNING: vmlinux.o(.text+0x11458): Section mismatch in reference from the function swiotlb_alloc_boot() to the function .init.text:__alloc_bootmem_low()
    The function swiotlb_alloc_boot() references
    the function __init __alloc_bootmem_low().
    This is often because swiotlb_alloc_boot lacks a __init
    annotation or the annotation of __alloc_bootmem_low is wrong.

    WARNING: vmlinux.o(.text+0x1011f2): Section mismatch in reference from the function swiotlb_late_init_with_default_size() to the function .init.text:__alloc_bootmem_low()
    The function swiotlb_late_init_with_default_size() references
    the function __init __alloc_bootmem_low().
    This is often because swiotlb_late_init_with_default_size lacks a __init
    annotation or the annotation of __alloc_bootmem_low is wrong.

and indeed the functions calling __alloc_bootmem_low() can be marked
__init as well.
Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/pci-swiotlb_64.c

@@ -13,7 +13,7 @@
 
 int swiotlb __read_mostly;
 
-void *swiotlb_alloc_boot(size_t size, unsigned long nslabs)
+void * __init swiotlb_alloc_boot(size_t size, unsigned long nslabs)
 {
 	return alloc_bootmem_low_pages(size);
 }

lib/swiotlb.c

@@ -116,7 +116,7 @@ setup_io_tlb_npages(char *str)
 __setup("swiotlb=", setup_io_tlb_npages);
 /* make io_tlb_overflow tunable too? */
 
-void * __weak swiotlb_alloc_boot(size_t size, unsigned long nslabs)
+void * __weak __init swiotlb_alloc_boot(size_t size, unsigned long nslabs)
 {
 	return alloc_bootmem_low_pages(size);
 }