efi_loader: segfault in efi_clear_os_indications()

If we call efi_clear_os_indications() before initializing the memory store
for UEFI variables a NULL pointer dereference occurs.

The error was observed on the sandbox with:

    usb start
    host bind 0 sandbox.img
    load host 0:1 $kernel_addr_r helloworld.efi
    bootefi $kernel_addr_r

Here efi_resister_disk() failed due to an error in the BTRFS implementation.

Move the logic to clear EFI_OS_INDICATIONS_FILE_CAPSULE_DELIVERY_SUPPORTED
to the rest of the capsule code.

If CONFIG_EFI_IGNORE_OSINDICATIONS=y, we should still clear the flag.
If OsIndications does not exist, we should not create it as it is owned by
the operating system.

Fixes: 149108a3 ("efi_loader: clear OsIndications")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>