Update U-boot Support with SPI use

[aidangarske]

Description

• Add U-Boot SPI HAL support for native TPM communication
• Fix build compatibility for U-Boot environment

Testing

• Build wolfTPM with U-Boot (sandbox target) (Complete)
• Verified MMIO mode still works with swtpm/QEMU linux path fine
• Test SPI communication with TPM hardware (TODO)

Changes

hal/tpm_io.c

• Add U-Boot SPI HAL implementation (TPM2_IoCb_Uboot_SPI)
• Implement TIS SPI protocol with wait-state handling (WOLFTPM_CHECK_WAIT_STATE)
• Add configurable SPI bus/CS via TPM_SPI_BUS, TPM_SPI_CS, TPM_SPI_MAX_HZ
• Use U-Boot's spi_get_bus_and_cs() and spi_xfer() APIs

src/tpm2.c

• Guard close(ctx->fd) with !defined(UBOOT) to prevent build error (U-Boot doesn't have file descriptors in this context)

Configuration

When UBOOT is defined:

• Uses U-Boot's SPI driver model via <spi.h> and <dm/uclass.h>
• SPI settings configurable in user_settings.h or board config
• Supports both wait-state polling and direct transfer modes