[platform][zynq][gem] make rx path more robust

- handle multiple packets per wakeup
- signal with an event
- seems to resolve my "network gets slow" issues
[app][stringtests] clean up the old asm files, make sure modern memset/memcopy works

Add reference C implementation to test/benchmark against.
[lib][minip] fully validate incoming ipv4 packets

Check length, checksum, and the target address being properly addressed.
[minip] Update udp chksum code to fit new struct layouts
[zynq] Move SLCR access to a struct layout, update clock interface
[gem]/[minip] mac and console changes

+ Add gem_set_macaddr
+ Disable promiscuous mode
+ Change flood command to raw
+ Change gem's console command from 'g' to 'gem'
+ Add status commands for both minip and gem
[bits] Add BIT_MASK macro
[minip] Don't add 0.0.0.0 to the arp table
init rework wip