target/ppc: Cache per-pmc insn and cycle count settings

This is the combination of frozen bit and counter type, on a per
counter basis. So far this is only used by HFLAGS_INSN_CNT, but
will be used more later.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
[danielhb: fixed PMC4 cyc_cnt shift, insn run latch code,
           MMCR0_FC handling, "PMC[1-6]" comment]
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220103224746.167831-2-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>