Current net-next/main does not boot for older chipsets e.g. Stratus.

Sample dmesg:
[   11.368315] bnxt_en 0000:02:00.0 (unnamed net_device) (uninitialized): Able to reserve only 0 out of 9 requested RX rings
[   11.390181] bnxt_en 0000:02:00.0 (unnamed net_device) (uninitialized): Unable to reserve tx rings
[   11.438780] bnxt_en 0000:02:00.0 (unnamed net_device) (uninitialized): 2nd rings reservation failed.
[   11.487559] bnxt_en 0000:02:00.0 (unnamed net_device) (uninitialized): Not enough rings available.
[   11.506012] bnxt_en 0000:02:00.0: probe with driver bnxt_en failed with error -12

This is caused by bnxt_get_avail_msix() returning a negative value for
these chipsets not using the new resource manager i.e. !BNXT_NEW_RM.
This in turn causes hwr.cp in __bnxt_reserve_rings() to be set to 0.

In the current call stack, __bnxt_reserve_rings() is called from
bnxt_set_dflt_rings() before bnxt_init_int_mode(). Therefore,
bp->total_irqs is always 0 and for !BNXT_NEW_RM bnxt_get_avail_msix()
always returns a negative number.

Historically, MSIX vectors were requested by the RoCE driver during
run-time and bnxt_get_avail_msix() was used for this purpose. Today,
RoCE MSIX vectors are statically allocated. bnxt_get_avail_msix() should
only be called for the BNXT_NEW_RM() case to reserve the MSIX ahead of
time for RoCE use.

bnxt_get_avail_msix() is also be simplified to handle the BNXT_NEW_RM()
case only.

Fixes: d630624e ("bnxt_en: Utilize ulp client resources if RoCE is not registered")
Signed-off-by: David Wei <dw@davidwei.uk>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20240502203757.3761827-1-dw@davidwei.ukSigned-off-by: Jakub Kicinski <kuba@kernel.org>