UEFI target groundwork: add device/uefi and device/amd64

[sparques]

Split from https://github.com/tinygo-org/tinygo/pull//5452

This pr adds the device/uefi and device/amd64 packages.

UEFI definitions and tables were pulled directly from the UEFI spec: https://uefi.org/specs/UEFI/2.11/

• Adds basic UEFI type definitions, table layouts, boot/runtime service structs, EFI status constants, and status-to-error mapping in uefi/efidef.go, uefi/efistatus.go, and uefi/tables.go.
• Adds amd64 assembly trampolines for calling UEFI functions with 0-10 arguments using the UEFI/MS x64 calling convention in uefi/asm_amd64.S, exposed through uefi/call.go.
• Adds UEFI initialization/access helpers for the system table, boot services, and image handle in uefi/util.go.
• Adds simple text output protocol bindings plus io.Writer-style console/stderr wrappers in uefi/simple_text_out.go and uefi/text_output.go.
• Adds UTF-8/UTF-16 CHAR16 conversion helpers in uefi/char16.go. (This one is weird, but I wanted to keep all the UEFI weirdness contained in the the uefi package)
• Adds TSC-based timing support for UEFI, including CPU pause/read-TSC helpers and TSC frequency detection/calibration via CPUID or a UEFI timer event in amd64/cpu.go, amd64/cpu_amd64.S, uefi/arch_x86.go, and uefi/clock.go.

This is purely additive so nothing existing should be affected by this PR.