[padctrl] Remove padctrl sources and merge functionality into pinmux

Note that hw/ip/padctrl still contains some legacy documentation
material and design sources that need to be moved or merged with the
pinmux docs. This will be done in a separate PR.

Signed-off-by: Michael Schaffner <msf@opentitan.org>
diff --git a/util/topgen-fusesoc.py b/util/topgen-fusesoc.py
index c864032..ba2936b 100644
--- a/util/topgen-fusesoc.py
+++ b/util/topgen-fusesoc.py
@@ -90,7 +90,7 @@
     # example, flash_ctrl depends on topgen but also on pwrmgr_pkg which depends on
     # pwrmgr_reg_pkg generated by topgen.
     if reg_only:
-        for ip in ['alert_handler', 'clkmgr', 'flash_ctrl', 'padctrl', 'pinmux', 'pwrmgr',
+        for ip in ['alert_handler', 'clkmgr', 'flash_ctrl', 'pinmux', 'pwrmgr',
                    'rstmgr', 'rv_plic']:
             core_filepath = os.path.abspath('generated-%s.core' % ip)
             name = 'lowrisc:ip:%s_reggen' % ip,