Set moea64_bpvo_pool_size based on physical memory

[afscoelho_gmail.com]

Summary

Currently moea64_bpvo_pool_size has a hard coded value of 327680 which is insufficient for initial memory mapping at boot time on systems with, for example, 64G and no huge pages enabled. This patch sets moea64_bpvo_pool_size value based on physical memory plus an expansion factor.
The value estimation for moea64_bpvo_pool_size uses the physical memory and page size as input:

pages = physmem / PAGE_SIZE;
size = pages * sizeof(vm_page);
moea64_bpvo_pool_size = size / PAGE_SIZE * BPVO_POOL_EXPANSION_FACTOR;

Test Plan

For tests, use tool "stress" to allocate memory and see if no panic "bpvo pool exhausted" is raised.
Patch https://reviews.freebsd.org/rS358670 is necessary when stress testing.

[afscoelho_gmail.com]

Adjust moea64_bpvo_pool_size value only if hw_direct_map is false, otherwise set it to previous hard-coded value.

[jhibbits]

sys/powerpc/aim/mmu_oea64.c

922

This needs to be a '== 0', since moea64_bpvo_pool_size is an integer used as an integer, not a boolean.

927

I'd make the 327680 a #define, commented that it's a sane historical default.

[luporl]

sys/powerpc/aim/mmu_oea64.c

924

It seems you are indenting with 2 spaces, but tabs should be used instead, except when you wrap long statements (as in the line below), then you should add 4 spaces.
Check style(9).

[afscoelho_gmail.com]

Style (indentation, comparison) fixes.

[alfredo]

sys/powerpc/aim/mmu_oea64.c

928

I think would be good print a message containing pool size and memory used by this pool when kernel boots is in verbose mode (boot -v).
Something like:

if (bootverbose)
    printf(".....\n");

[afscoelho_gmail.com]

sys/powerpc/aim/mmu_oea64.c

928

Good idea, thanks.

[afscoelho_gmail.com]

sys/powerpc/aim/mmu_oea64.c

928

It looks like it's not possible to use 'bootverbose' at this stage of the boot. This variable is set later by init_main.c:129.

[jhibbits]

sys/powerpc/aim/mmu_oea64.c

928

(boothowto & RB_VERBOSE) does the same thing, and should be available almost immediately.

[afscoelho_gmail.com]

Print information message about number of bpvo pool entries and memory used by this pool when booting in verbose mode.

[alfredo]

LGTM