bnxt_en: Fix build break on non-x86 platforms

bnxt_en: Fix build break on non-x86 platforms

Commit c470195b989fe added .getcrosststamp() interface where
the code uses boot_cpu_has() function which is available only
in x86 platforms. This fails the build on any other platform.

Since the interface is going to be supported only on x86 anyway,
we can simply compile out the entire support on non-x86 platforms.

Cover the .getcrosststamp support under CONFIG_X86

Fixes: c470195b989f ("bnxt_en: Add PTP .getcrosststamp() interface to get device/host times")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202601111808.WnBJCuWI-lkp@intel.com
Signed-off-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20260113183422.508851-1-michael.chan@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>