[kmac] Let AppIntf run out of reset

This commit revises entropy module to run without SW out of reset. The
newly introduced AppIntf may accept the request before SW image is
loaded. Then SW may not be able to trigger kmac_entropy to prepare any
entropy.

By creating dummy entropies in StReset state, the AppIntf can initiates
the request and get the digest result.

Signed-off-by: Eunchan Kim <eunchan@opentitan.org>

hw/ip/kmac/rtl/kmac_entropy.sv

diff --git a/hw/ip/kmac/rtl/kmac_entropy.sv b/hw/ip/kmac/rtl/kmac_entropy.sv
index 8d0d524..818d503 100644
--- a/hw/ip/kmac/rtl/kmac_entropy.sv
+++ b/hw/ip/kmac/rtl/kmac_entropy.sv
@@ -407,6 +407,10 @@
     unique case (st)
       StRandReset: begin
         if (entropy_ready_i) begin
+
+          // As SW ready, discard current dummy entropy and refresh.
+          rand_valid_clear = 1'b 1;
+
           // SW has configured KMAC
           unique case (mode_i)
             EntropyModeSw: begin
@@ -429,6 +433,11 @@
           endcase
         end else begin
           st_d = StRandReset;
+
+          // Setting the dummy rand gate until SW prepares.
+          // This lets the Application Interface move forward out of reset
+          // without SW intervention.
+          rand_valid_set = 1'b 1;
         end
       end