hw/intc/armv7m_nvic: Implement cache ID registers

hw/intc/armv7m_nvic: Implement cache ID registers

M profile cores have a similar setup for cache ID registers
to A profile:
 * Cache Level ID Register (CLIDR) is a fixed value
 * Cache Type Register (CTR) is a fixed value
 * Cache Size ID Registers (CCSIDR) are a bank of registers;
   which one you see is selected by the Cache Size Selection
   Register (CSSELR)

The only difference is that they're in the NVIC memory mapped
register space rather than being coprocessor registers.
Implement the M profile view of them.

Since neither Cortex-M3 nor Cortex-M4 implement caches,
we don't need to update their init functions and can leave
the ctr/clidr/ccsidr[] fields in their ARMCPU structs at zero.
Newer cores (like the Cortex-M33) will want to be able to
set these ID registers to non-zero values, though.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180209165810.6668-6-peter.maydell@linaro.org