arm/aspeed: actually check RAM size

arm/aspeed: actually check RAM size

It's supposed that SOC will check if "-m" provided
RAM size is valid by setting "ram-size" property and
then board would read back valid (possibly corrected
value) to map RAM MemoryReging with valid size.
It isn't doing so, since check is called only
indirectly from
  aspeed_sdmc_reset()->asc->compute_conf()
or much later when guest writes to configuration
register.

So depending on "-m" value QEMU end-ups with a warning
and an invalid MemoryRegion size allocated and mapped.
(examples:
 -M ast2500-evb -m 1M
    0000000080000000-000000017ffffffe (prio 0, i/o): aspeed-ram-container
      0000000080000000-00000000800fffff (prio 0, ram): ram
      0000000080100000-00000000bfffffff (prio 0, i/o): max_ram
 -M ast2500-evb -m 3G
    0000000080000000-000000017ffffffe (prio 0, i/o): aspeed-ram-container
      0000000080000000-000000013fffffff (prio 0, ram): ram
      [DETECTED OVERFLOW!] 0000000140000000-00000000bfffffff (prio 0, i/o): max_ram
)
On top of that sdmc falls back and reports to guest
"default" size, it thinks machine should have.

This patch makes ram-size check actually work and
changes behavior from a warning later on during
machine reset to error_fatal at the moment SOC.ram-size
is set so user will have to fix RAM size on CLI
to start machine.

It also gets out of the way mutable ram-size logic,
so we could consolidate RAM allocation logic around
pre-allocated hostmem backend (supplied by user or
auto created by generic machine code depending on
supplied -m/mem-path/mem-prealloc options.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200219160953.13771-10-imammedo@redhat.com>