efi_loader: Improve EFI variable load message

efi_loader: Improve EFI variable load message

Change the EFI variable load message from log_err() to log_info() with
neutral wording. The previous "Failed to load" message caused customer
confusion as it appeared to indicate an error condition.

The efi_var_from_file() function deliberately returns EFI_SUCCESS in
this case to allow the boot process to continue normally. This is
documented in the function's comment block but was not reflected in
the log message level or content.

The message now uses informational wording to reflect that this is
normal behavior when the ubootefi.var file does not yet exist.

Signed-off-by: Pranav Tilak <pranav.vinaytilak@amd.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>