x86/cpu: Remove LASS restriction on vsyscall emulation

Vsyscall emulation has two modes of operation: XONLY and EMULATE. The
default XONLY mode is now supported with a LASS-triggered #GP. OTOH,
LASS is disabled if someone requests the deprecated EMULATE mode via the
vsyscall=emulate command line option. So, remove the restriction on LASS
when the overall vsyscall emulation support is compiled in.

As a result, there is no need for setup_lass() anymore. LASS is enabled
by default through a late_initcall().

Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Reviewed-by:
Tested-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Link: https://patch.msgid.link/20260309181029.398498-6-sohil.mehta@intel.com