pmtools: support huge ACPI table

For some servers such as Canoe Pass or Thunder Ridge, they have much
more entries in ACPI table, so original 1K buffer is insufficient.

Switch to dynamic buffer for this situation.

Remove 'protocol' field in SRC_URI as well which cause warning:

| WARNING: Failed to fetch URL git://github.com/anyc/pmtools.git;protocol=https

,
| attempting MIRRORS if available

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>