swmbx: Introduce mailbox target driver

[stevenlee7189]

Introduce software mailbox driver, which enables the BMC to
communicate with the Root of Trust (RoT) over an I2C target interface.

Execute the following command at the BMC prompt to verify SWMBX functionality:

• Verify the SWMBX address:
  aspeed-pfr-tool -w 0x13 0x8
  aspeed-pfr-tool -r 0x13
  [Expected output: 0x8]

• Verify the protected SWMBX address:
  aspeed-pfr-tool -w 0x12 0x8
  aspeed-pfr-tool -r 0x12
  [Expected output: 0x0]

• Verify the notify functionality:
  aspeed-pfr-tool -w 0x13 0x8
  On Ast1060 console, you should see [NOTIFY] SWMBX: notify triggered on port 0 addr 0x13

• Verify the FIFO functionality:
  aspeed-pfr-tool -w 0xd 0x1f
  aspeed-pfr-tool -w 0xd 0x2f
  aspeed-pfr-tool -w 0xd 0x3f
  aspeed-pfr-tool -r 0xd
  aspeed-pfr-tool -r 0xd
  aspeed-pfr-tool -r 0xd
  aspeed-pfr-tool -r 0xd
  [Expected output: 0x1f, 0x2f, 0x3f, 0x0]

[stevenlee7189]

The PR should be reviewed after the i2c driver is merged.

[stevenlee7189]

Test Step on ast1060_prot evb:

First PROT module: running the PFR firmware:
https://github.com/AspeedTech-BMC/aspeed-zephyr-project/releases/download/v03.02/ast1060_prot_v03.02.tgz
Second PROT module: running the Rust firmware:
uart_ast10x0_swmbx.zip

When the second PROT module starts, it shows the following log:

####### SWMBX test #######


## SWMBX: Starting up...

[SWMBX] enable_behavior: 0x0 -> 0x7

After the second PROT module boots up, you should see a device with address 0x38 appear on I²C bus 1 of the first PROT module.

uart:~$ iic scan i2c@7e7b0080
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:             -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- 38 -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
1 devices found on i2c@7e7b0080

Then, run the following mailbox test commands from the first PROT module:

• mailbox read/write test

uart:~$ iic write_byte i2c@7e7b0080 38 13 88
uart:~$ iic read_byte i2c@7e7b0080 38 13
Output: 0x88

• mailbox fifo test

uart:~$ iic write_byte i2c@7e7b0080 38 d aa
uart:~$ iic write_byte i2c@7e7b0080 38 d bb
uart:~$ iic write_byte i2c@7e7b0080 38 d cc
uart:~$ iic write_byte i2c@7e7b0080 38 d dd
uart:~$ iic read_byte i2c@7e7b0080 38 d
Output: 0xaa
uart:~$ iic read_byte i2c@7e7b0080 38 d
Output: 0xbb
uart:~$ iic read_byte i2c@7e7b0080 38 d
Output: 0xcc
uart:~$ iic read_byte i2c@7e7b0080 38 d
Output: 0xdd
uart:~$ iic read_byte i2c@7e7b0080 38 d
Output: 0x0