xtensa: remove unnecessary padding in arch_mem_domain

[ldmstm]

Is your enhancement proposal related to a problem? Please describe.
The current definition of arch_mem_domain for the xtensa architecture (

zephyr/include/zephyr/arch/xtensa/arch.h

Line 65 in 023248a

uint32_t *ptables __aligned(CONFIG_MMU_PAGE_SIZE);

) forcefully aligns one of its members to a page boundary, adding unnecessary padding.

I suspect the intention behind this alignment is to indicate the pointer points to an MMU page-size aligned address, but instead it aligns the pointer storage itself.

Describe the solution you'd like
The __aligned directive needs to be removed.

[dcpleung]

Reopening this for backporting to v3.7