firmware: thead: Fix buffer overflow and use standard endian macros

In the Linux kernel, the following vulnerability has been resolved:

firmware: thead: Fix buffer overflow and use standard endian macros

Addresses two issues in the TH1520 AON firmware protocol driver:

1. Fix a potential buffer overflow where the code used unsafe pointer
arithmetic to access the 'mode' field through the 'resource' pointer
with an offset. This was flagged by Smatch static checker as:
"buffer overflow 'data' 2 <= 3"

2. Replace custom RPC_SET_BE* and RPC_GET_BE* macros with standard
kernel endianness conversion macros (cpu_to_be16, etc.) for better
portability and maintainability.

The functionality was re-tested with the GPU power-up sequence,
confirming the GPU powers up correctly and the driver probes
successfully.

[ 12.702370] powervr ffef400000.gpu: [drm] loaded firmware
powervr/rogue_36.52.104.182_v1.fw
[ 12.711043] powervr ffef400000.gpu: [drm] FW version v1.0 (build
6645434 OS)
[ 12.719787] [drm] Initialized powervr 1.0.0 for ffef400000.gpu on
minor 0