[rtl872x] SPI and UART HAL minor fix.

[XuGuohui]

Problem

1. SPI slave is busy once enabled
2. Providing unaligned ring buffer for UART will result initialization failure

Solution

1. Only check the busy status for SPI master mode
2. Make sure the aligned size is smaller than the given buffer size

Steps to Test

1. wiring/no_fixture_spi
2. Run the attached test app

Example App

#include <iostream>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <memory>
#include <cstring>
#include <chrono>

uint8_t __attribute__((aligned(4))) buf[168];
size_t bufLen = sizeof(buf);

int main(int argc, char* argv[]) {
    void* pBuf = buf;
    size_t alignment = 32;
    size_t size = bufLen;
    
    void* newPtr = std::align(alignment, size, pBuf, bufLen);
    printf("PTR: %08X -> %08X, %d\r\n", (uint32_t)buf, (uint32_t)newPtr, (uint8_t*)newPtr - (uint8_t*)buf);
    printf("After aligned: %d\r\n", bufLen);

    size = bufLen - alignment;
    newPtr = std::align(alignment, size, pBuf, bufLen);
    printf("PTR: %08X -> %08X, %d\r\n", (uint32_t)buf, (uint32_t)newPtr, (uint8_t*)newPtr - (uint8_t*)buf);
    printf("After aligned: %d\r\n", bufLen);
    return 0;
}

References

N/A

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)