efi/libstub: Bump up EFI_MMAP_NR_SLACK_SLOTS to 32

Recent platforms require more slack slots than the current value of
EFI_MMAP_NR_SLACK_SLOTS, otherwise they fail to boot. The current
workaround is to append `efi=disable_early_pci_dma` to the kernel's
cmdline. So, bump up EFI_MMAP_NR_SLACK_SLOTS to 32 to allow those
platforms to boot with the aforementioned workaround.

Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Allen Pais <apais@linux.microsoft.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Author: effective-light

drivers/firmware/efi/libstub/efistub.h

@@ -171,7 +171,7 @@ void efi_set_u64_split(u64 data, u32 *lo, u32 *hi)
  * the EFI memory map. Other related structures, e.g. x86 e820ext, need
  * to factor in this headroom requirement as well.
  */
-#define EFI_MMAP_NR_SLACK_SLOTS	8
+#define EFI_MMAP_NR_SLACK_SLOTS	32
 
 typedef struct efi_generic_dev_path efi_device_path_protocol_t;