hw/arm/aspeed: Split AST1030 EVB machine into a separate source file for maintainability

hw/arm/aspeed: Split AST1030 EVB machine into a separate source file for maintainability

This commit moves the Aspeed AST1030 MiniBMC machine
implementation out of aspeed.c into a new standalone file
aspeed_ast10x0_evb.c.

This refactor continues the modularization effort for Aspeed platform
support, placing each board’s logic and initialization sequence in its
own dedicated source file. It improves maintainability, readability, and
makes it easier to extend support for additional AST10x0-based variants.

Key updates include:
- Moved aspeed_minibmc_machine_init() and
  aspeed_minibmc_machine_ast1030_evb_class_init() from aspeed.c to
  aspeed_ast10x0_evb.c.
- Moved ast1030_evb_i2c_init() and associated I2C setup code.
- Removed AST1030 EVB machine type registration from aspeed.c.
- Added aspeed_ast10x0_evb.c to the Meson build system (meson.build).

No functional changes.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20251104031325.146374-31-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>