KVM: arm64: nv: Honor SError routing effects of SCTLR2_ELx.NMEA

KVM: arm64: nv: Honor SError routing effects of SCTLR2_ELx.NMEA

As the name might imply, when NMEA is set SErrors are non-maskable and
can be taken regardless of PSTATE.A. As is the recurring theme with
DoubleFault2, the effects on SError routing are entirely backwards to
this.

If at EL1, NMEA is *not* considered for SError routing when TMEA is set
and the exception is taken to EL2 when PSTATE.A is set.

Link: https://lore.kernel.org/r/20250708172532.1699409-20-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>