boards: x86/minnowboard: specify CONFIG_X86_MMU_PAGE_POOL_PAGES

Given that the Minnowboard has relatively large memory, the default
number of pages allocated for page tables are not enough, and
resulting in asserting in the page table initialization code.
So change the number of pages to a large number to accomodate
various applications.

Fixes #24353

Signed-off-by: Daniel Leung <daniel.leung@intel.com>