gicv3: fix ICH_MISR's LRENP computation

According to the "Arm Generic Interrupt Controller Architecture
Specification GIC architecture version 3 and 4" (version G: page 345
for aarch64 or 509 for aarch32):
LRENP bit of ICH_MISR is set when ICH_HCR.LRENPIE==1 and
ICH_HCR.EOIcount is non-zero.

When only LRENPIE was set (and EOI count was zero), the LRENP bit was
wrongly set and MISR value was wrong.

As an additional consequence, if an hypervisor set ICH_HCR.LRENPIE,
the maintenance interrupt was constantly fired. It happens since patch
9cee1efe ("hw/intc: Set GIC maintenance interrupt level to only 0 or 1")
which fixed another bug about maintenance interrupt (most significant
bits of misr, including this one, were ignored in the interrupt trigger).

Fixes: 83f036fe ("hw/intc/arm_gicv3: Add accessors for ICH_ system registers")
Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20211207094427.3473-1-damien.hedde@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>