Integration of I2C block

[alees24]

This PR integrates the I2C block from the OpenTitan project, and updates the software accordingly:

• RTL changes for I2C integration into FPGA and Verilator simulation
• Vendor in I2C block from OT project (please check; vendoring and patch file creation is unfamiliar)
• Modify existing software base (sw/c/common) to use the OpenTitan UART for output
• Introduce simplified I2C driver software for the OT I2C block; this is based on the code from the OT project but is rewritten to be simpler, more compact and have no dependencies such as 'base', and 'lib/dif' etc.
• Create a small test application 'i2c_hat_id' that reads and reports the contents of the ID EEPROM present on standard-compliant RaspberryPi HATs.

Please note that this demo will not run properly in Verilator simulation because there is presently no I2C DPI model to act as the target device, but may be run on Sonata FPGA by tying the 'cheri_en' low in sonata_system.sv. This code is intended not just to test the operation of the integrated block but also to serve as a guide for CHERIoT driver/application development.

[marnovandermaas]

I tested this on FPGA by tying cheri_en to zero and set the SRAMInitFile to the location of i2c_hat_id.vmem. Then I see the following UART output:

i2c_hat_id demo application
clk_period: 40
thigh:   100
tlow:    126
t_f:     1
t_r:     3
thd_sta: 100
tsu_sta: 118
thd_dat: 125
tsu_dat: 7
t_buf:   119
tsu_sto: 100
00000000 : 52 2D 50 69 01 00 03 00 F0 03 00 00 01 00 00 00 : R-Pi............
00000010 : 2D 00 00 00 E7 58 D1 95 F1 56 28 AB CB 4E 99 42 : -....X...V(..N.B
00000020 : C7 79 D6 A3 01 00 01 00 0C 09 52 61 73 70 62 65 : .y........Raspbe
00000030 : 72 72 79 20 50 69 53 65 6E 73 65 20 48 41 54 7F : rry PiSense HAT.
00000040 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 : ................
00000050 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 : ................
00000060 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 : ................
00000070 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 : ................
EXCEPTION!!!
============
MEPC:   0x00101222
MCAUSE: 0x00000007
MTVAL:  0x00020008