qemu-log: new option -dfilter to limit output

When debugging big programs or system emulation sometimes you want both
the verbosity of cpu,exec et all but don't want to generate lots of logs
for unneeded stuff. This patch adds a new option -dfilter which allows
you to specify interesting address ranges in the form:

  -dfilter 0x8000..0x8fff,0xffffffc000080000+0x200,...

Then logging code can use the new qemu_log_in_addr_range() function to
decide if it will output logging information for the given range.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <1458052224-9316-7-git-send-email-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
