x86: Fix some memory sizes when setting up bios

In e820_setup(), the memory region of MB_BIOS is [MB_BIOS_BEGIN, MB_BIOS_END],
so its memory size should be MB_BIOS_SIZE (= MB_BIOS_END - MB_BIOS_BEGIN + 1).
The same thing goes for BDA, EBDA, MB_BIOS and VGA_ROM in setup_bios().
By the way, a little change is made in setup_irq_handler() to avoid using
hard coding.

Signed-off-by: Sicheng Liu <lsc2001@outlook.com>
Link: https://lore.kernel.org/r/SY6P282MB373318D6241D56E074B040DFA3392@SY6P282MB3733.AUSP282.PROD.OUTLOOK.COM


Signed-off-by: Will Deacon <will@kernel.org>