riscv: plic: Add a couple of mising sifive_plic_update calls

Claiming an interrupt and changing the source priority both potentially
affect whether an interrupt is pending, thus we must re-compute xEIP.
Note that we don't put the sifive_plic_update inside sifive_plic_claim
so that the logging of a claim (and the resulting IRQ) happens before
the state update, making the causal effect clear, and that we drop the
explicit call to sifive_plic_print_state when claiming since
sifive_plic_update already does that automatically at the end for us.

This can result in both spurious interrupt storms if you fail to
complete an IRQ before enabling interrupts (and no other actions occur
that result in a call to sifive_plic_update), but also more importantly
lost interrupts if a disabled interrupt is pending and then becomes
enabled.

Signed-off-by: Jessica Clarke <jrtc27@jrtc27.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20200618210649.22451-1-jrtc27@jrtc27.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>