thunderbolt: Add uaccess dependency to debugfs interface

Some calls in the debugfs interface are made to the linux/uaccess.h header,
but the header is not referenced. So, for x86_64 architectures, this
dependency seems to be pulled in elsewhere, which leads to a successful
compilation. However, on arm/arm64 architectures, it was found to error out
on implicit declarations.

This change fixes the implicit declaration error by adding the
linux/uaccess.h header.

Fixes: 54e41810 ("thunderbolt: Add debugfs interface")
Signed-off-by: Casey Bowman <casey.g.bowman@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>