hamradio: baycom_epp: fix build for UML

On i386, the baycom_epp driver wants to inspect X86 CPU features (TSC)
and then act on that data, but that info is not available when running
on UML, so prevent that test and do the default action.

Prevents this build error on UML + i386:

../drivers/net/hamradio/baycom_epp.c: In function ‘epp_bh’:
../drivers/net/hamradio/baycom_epp.c:630:6: error: implicit declaration of function ‘boot_cpu_has’; did you mean ‘get_cpu_mask’? [-Werror=implicit-function-declaration]
  if (boot_cpu_has(X86_FEATURE_TSC))   \
      ^
../drivers/net/hamradio/baycom_epp.c:658:2: note: in expansion of macro ‘GETTICK’
  GETTICK(time1);

Fixes: 68f5d3f3 ("um: add PCI over virtio emulation driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: linux-um@lists.infradead.org
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Thomas Sailer <t.sailer@alumni.ethz.ch>
Cc: linux-hams@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>