Change FIT_KERNEL_COMP_ALG to lzma

This change is applied to all aarch64 platforms.

Reduce compressed kernel size for Google BMC.

Tested:
```
  ┌────────────────────┬─────────────┬─────────────┬─────────────────┐
  │ Metric             │ Prod (Gzip) │ Prod (LZMA) │ Reduction       │
  ├────────────────────┼─────────────┼─────────────┼─────────────────┤
  │ Uncompressed Image │ 11.28 MiB   │ 11.28 MiB   │ -               │
  │ Compressed Kernel  │ 4.86 MiB    │ 3.63 MiB    │ ~1.23 MiB (25%) │
  │ Full FIT Image     │ 6.07 MiB    │ 4.84 MiB    │ ~1.23 MiB       │
  └────────────────────┴─────────────┴─────────────┴─────────────────┘
```

Tested:
- platform11: https://fusion2.corp.google.com/ab1d2f1f-08da-3352-b24b-328bc8d2e2a0
- platform11: https://fusion2.corp.google.com/19c963e7-860e-3a12-844d-cf7e84fe7492
- platform5: https://fusion2.corp.google.com/78a00bbd-ba49-3a62-bf28-63f9a550f01a
- platform15: https://fusion2.corp.google.com/4fc481c8-15fa-3382-93fd-7b3f3401f745
- platform17: https://fusion2.corp.google.com/d449fef1-c631-353b-a241-0d21b2a7cd5f
- platform18: https://fusion2.corp.google.com/2939bcb2-59cf-3c16-999f-412d77dc24fb
Google-Bug-Id: 512539812
Change-Id: I8ddc80c57adc5c831cb9cfa675733e1dbb0d5780
Signed-off-by: Willy Tu <wltu@google.com>