KVM: PPC: Book3S HV nestedv2: Ensure LPCR_MER bit is passed to the L0

LPCR_MER is conditionally set during entry to a guest if there is a
pending external interrupt. In the nestedv2 case, this change is not
being communicated to the L0, which means it is not being set in the L2.
Ensure the updated LPCR value is passed to the L0.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231201132618.555031-6-vaibhav@linux.ibm.com