cpu/xtensa.cpp, skeleton/hudson_poems.cpp: Added initial emulation for CPU core, and Poems hardware that utilizes it [David Haywood]

[mamehaze]

xtensa.cpp

• implemented an execution core with support for feature level required by hudson/konami PLAY-POEMS hardware
• fixed a number of bugs in the disassembler

hudson_poems.cpp

• got Marimba Tengoku to boot
• reverse engineered many functions of the video hardware (4 tilemaps, sprites etc.) and created a preliminary implementation

[rb6502]

This looks pretty reasonable at a first run-through. Two general notes:

1. Search-and-replace the few instances of full types in the xtensa stuff (uint32_t) for the short u8/u16/u32 forms the majority of the code's using.

2. For pulling fields out of the opcode and not modifying them again (reg_s, reg_r, that kind of thing) make those variables const. Every little bit we can help the compiler is good, especially in CPU cores.

[mamehaze]

This looks pretty reasonable at a first run-through. Two general notes:

1. Search-and-replace the few instances of full types in the xtensa stuff (uint32_t) for the short u8/u16/u32 forms the majority of the code's using.

2. For pulling fields out of the opcode and not modifying them again (reg_s, reg_r, that kind of thing) make those variables const.  Every little bit we can help the compiler is good, especially in CPU cores.

done and done

[cuavas]

This mostly looks fine. Just a few relatively easy things and it’ll be mergeable.