lm32: add Milkymist HPDMC support

This patch adds support for the Milkymist's High Performance Dynamic Memory
Controller. This is just a dumb model without any functionality. While the
real hardware acts for example as a bridge between software and hardware
for sending SDRAM commans, this model will only eat up these commands and
always returns the expected hardware states, eg. PLL locked etc.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>

trace-events

diff --git a/trace-events b/trace-events
index fc8caa8..9ccf82c 100644
--- a/trace-events
+++ b/trace-events
@@ -298,3 +298,7 @@
 disable milkymist_ac97_in_cb_transferred(int transferred) "transferred %d"
 disable milkymist_ac97_out_cb(int free, uint32_t remaining) "free %d remaining %u"
 disable milkymist_ac97_out_cb_transferred(int transferred) "transferred %d"
+
+# hw/milkymist-hpdmc.c
+disable milkymist_hpdmc_memory_read(uint32_t addr, uint32_t value) "addr %08x value %08x"
+disable milkymist_hpdmc_memory_write(uint32_t addr, uint32_t value) "addr %08x value %08x"