meta-bletchley: add 99-platform-init

Add 99-platform-init to archive following items
1. Disable FMC_WDT2
AST2600 use FMC_WDT2 to archive ABR feature.
Disable FMC_WDT2 before systemd start.

2. Detec

meta-bletchley: add 99-platform-init

Add 99-platform-init to archive following items
1. Disable FMC_WDT2
AST2600 use FMC_WDT2 to archive ABR feature.
Disable FMC_WDT2 before systemd start.

2. Detect boot flash source
Write boot source into /run/media/slot
0: boot from primary
1: boot from alternate

Tested result:
- In u-boot, FMC_WDT2 is enabled and timer is counting down
```
U-Boot 2019.04 (Nov 10 2022 - 00:12:58 +0000)

SOC: AST2620-A3
RST: WDT1 SOC
PCI RST: #2
RST: External
FMC 2nd Boot (ABR): Enable, Dual flashes, Source: Primary
Set FMC_WDT2 timer reload value to 0x0BB8
eSPI Mode: SIO:Enable : SuperIO-2e
Eth: MAC0: RMII/NCSI, MAC1: RMII/NCSI, MAC2: RGMII, MAC3: RMII/NCSI
Model: Facebook Bletchley BMC
DRAM: already initialized, 2 GiB (capacity:2048 MiB, VGA:0 MiB, ECC:off)
MMC:
Loading Environment from SPI Flash... SF: Detected w25q01jv with page size 256 Bytes, erase size 4 KiB, total 128 MiB
*** Warning - bad CRC, using default environment

In: serial@1e784000
Out: serial@1e784000
Err: serial@1e784000
Model: Facebook Bletchley BMC
Net: Could not get PHY for eth2: addr 0
Failed to initialize PHY: -19
eth-1: ftgmac@1e670000
Hit any key to stop autoboot: 0
ast# md.l 0x1e620064 2
1e620064: 00000001 0b560bb8 ......V.
```

- After BMC boot into Linux OS, FMC_WDT2 is disabled
```
bletchley login: root
Password:
root@bletchley:~# devmem 0x1e620064
0x00000000
root@bletchley:~# devmem 0x1e620068
0x0BB80BB8
```

- check boot source (primary)
```
root@bletchley:~# cat /run/media/slot
0
```

Signed-off-by: Potin Lai <potin.lai@quantatw.com>
Change-Id: If5e41dd9745ba5c4ec45637772136e847954c56e

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